(The original email this was answering has been misplaced. If I locate it, I'll add it here.)
Not sure I'd know how to figure an answer out for this, but I can tell you of a test I tried first of the month. I put out a new title, than sent the link for it to the 2,400 of my more devoted fans (I've 7,000 who buy stuff off and on, but of those only 2,400 buy more or less regular, and these are also the ones who interact with me on social networks and show up at car shows and book signings to hang out with me during events - I've meet most of these 2,400 people, some of them more than once; however as I rarely tell anyone I've released a new title it can take a few months before sales trickle in). Anyways, usually I just publish a new title than start working on the next one. I don't announce the new release, don't email anyone the link, nothing. Sales are sporadic, rarely start the first week, and can take a few weeks to start. (Short stories so, this is typical.)
However, for this title, I decided to send out a message announcing it (I've never done that before). So I did my usual weekly update of "Here's what happened to me, here's new pics of my cats, here's what my dog's been up to, here are the latest shows my cars will be featured in, here's my latest rant on the current lack health care conditions in Maine, along with the latest LePage veto on Medicare, more doctors gone on strike, 70,000 more Mainers lost health insurance this week, record breaking lines at the free clinic due to the ER turning away so many uninsured folks (I know I was one of them, broke my leg, took 3 weeks of waiting in line at the clinic to get it checked because the ER is basically out of operation) long rave and rant on medical strike and the fact that there are lines of people outside the hospital trying to get in, why are doctors allowed to go on strike, Veterans hospital is now taking non Veteran emergency patients, their doctors are declaring Maine in a medical crisis, blah, blah, blah, ...and Oh, by the way, I just released a new title, here it is...."
At the end of the day I checked my dashboard and saw that title had 27 sales. That's a little over 1% of my "die-hard fans" who bought the book the first day as a direct result of the announcement. That's the same total I can usually expect to see across the entire first month, as 1 or 2 sales a day, not every day, is pretty typical for my short stories.
Not sure that that means anything to help with your question or not. How does 27 sales out of 2,400 fans translate into:
To answer A: Well for the title in question, it was a 2,500 word short that took me about 7 hours to write. I wrote it one day. Edited it the next day using a free editing software program. Created the cover using free images off of mourgefiles with a free photoshop-like program called ChasyDraw. So basically I didn't put any money into it at all. I put maybe 15 hours total into it's creation from start to finish. Okay, because no money was put into it, we'll just assume that the cost of the electricity/office/computer/other overhead is equal to minimum wage, for easy sake of argument.
Right now (2013) minimum wage is $5.13 per how. There is talk it'll increase to $7.30 soon. If I figure on minimum wage at $7.50 an hour x 15 hours, than I'll need to earn $112 per week to break even. However it's selling at .99c (because I automatically price everything under 5k words at .99c regardless of what it is.) So those 27 sales x 35% of .99c = just under $10. So I have to sell 330 copies to break even at minimum wage for this particular title.
However, I don't like minimum wage, so I'm going to say I want to be paid something a little more professional, let's say $15 an hour (twice minimum wage). Well that now means I'd have to sell 660 copies per week to break even.
To answer B: We continue from A, and every title sold past the 661st copy becomes profit. Is it enough to live on? Well, if it sells the typical average of 1 to 2 copies a day at .35c per sale, that's only an income of .70c per day, so no, that isn't enough to live on, not it it's the only title.
To make money is going to require a lot more sales, a lot more titles, and also titles priced at $2.99 or higher.
I figured it out once, and because I live in a motorhome my expenses are a 1/3 what they were when I used to live in a house. No electricity bill to pay any more. Plus I lack bills other authors have: No phone bill (near mute Autistic person without enough vocal ability to communicate effectively over a phone), no cable (seeing how I do not own a TV - I do own a portable DVD player and full season collections of MANY TV series to make up for the lack of a TV though.)
My gas bills are higher than most, however, due to the 200lbs of marbles glued to the hood of my daily driver Volvo which used to get 22mpg but now gets only 14mpg thanks to the weight and lack of air flow of the rhinestones/beads/marbles and than the 7mpg the RV gets, and I have no idea how much mpg the 22' 1964 Dodge police car gets, but when it eats more lead than gas and you have to mix your own gas because nobody sells leaded gas anymore, well whose counting miles anymore?
The only real bill I have is the comic book collection which requires a 48ft by 28ft storage unit to house. My comic books when bagged, boarded, and started are taller, longer, and wider than my motorhome and my car lined up end to end. I have a lot of comic books. They don't fit in the library either, I own a library, private collection, 12,000 books at last count several years ago.
I buy 800 books a month, I haven't dared recount - it takes months to do. Food wise, it's me, 12 cats, a rabbit, and a teeny-tiny dog who only comes up to the knees of the cats.
The biggest expense is the animal shelter - 500 cats, birds, and horses that take up 4 to 8 hours a day just to feed them all. (My partner, has his own house, I have phobia issues, a result of a bomb in my house, which is why I live in a RV now, seeing as I'm no longer able to set a feet in a house since the bomb. So he has a new house, where he lives and I live in a motorhome in the driveway for the past 7 years since the bomb.) Well my partner pays for the book storage and I'm slowly retiring from the shelter/rescue and my brother is doing more and more of the work, slowly taking over that business.
My health has become an issue and I simply can not run a massive animal rescue on that scale anymore, so by the end of the year I likely will still own but no longer be running the shelter.
In the end, with my partner paying for the books and the shelter changing hands, the only expenses I now have are gas for my cars and RV and food for me, the 12 cats, the rabbit, and the dog. I boondock, meaning I have no running water, no hook-ups, no electricity, no sewer. Nothing on board. Catlitter. A 30lb bag of dogfood last 6 months thats $24 a year. Catfood 36lbs a week at $18 a bag is $950 a year. Rabbit eats vegetable scraps from my food. My food $20 tp $50 a week = at most $2,000 a year. Gas? I'm pretty much permanently parked.
The RV rarely moves, when it does it's just to drive the cats around the neighborhood to keep the engine from sticking. I only go out to buy food once ever couple of months, and I attend events on weekends but none of those are far away, so I'm not using much more than $60 a month. I can (and have for the past 7 years) live quite well on an income of $200 to $600 a month.
Thing is I used to be very wealthy, and I still have all the rare books, insanely expensive cars, antique kimonos, and lots of furs, but the bomb did change me a lot. Hurricane Katrina took the house down and we started rebuilding, but 6 months the bomber arrived and the only stuff that survived the bomb was the stuff that was in storage. And $3million in medical bills later, we had no money to rebuild again. The bomb did more damage than what people are aware of. The $3million in medical bills those were just the first few weeks after the bomb...the bills are still rising. New bills arrive every month $13,000 a day for one machine. I stopped adding the totals up after it hit $3million. That was 7 years ago. I broke my leg 4 weeks ago - I was denied ER treatment, because my outstanding bill was too high. I was turned away from the free clinic 3 times.
I was homeless out of necessity for 6 months, and than I moved back indoors and discovered I had developed a massive, horrible phobia of being indoors. It was so bad, that I became "willfully" homeless, because I was unable to feel safe living indoors ever since the bomb. It took me 6 years living in my car to be able to progress to living in a motorhome. Will I ever work my way back up to living in a house again? I don't know. All I know is someone tried to kill me and my family and not everyone survived the bomb and 7 years later I'm still not able to function yet.
Money lost it's importance to me. I lost my husband. And my baby. Baby's dead, husband's not. He remembers me as very good friend. 21 years of marriage is gone. He has no memory of me as his wife, at all. He doesn't remember the baby either. He's alive but it's worse than if he was dead. To look in his eyes and see nothing. That's why money means nothing to me now. What I've lost money can't bring back.