Oh, so simple a question, yet the answer is so fraught with difficulties.
Having been faced with this question three times in as many weeks, I decided to write a short piece that I could attach to an email and send if asked again - but of course there is no short answer for so many elements depend one on another.
What I ended up with is longer than even I anticipated, so long in fact that I've given it its own Page on this site. If you really want the answer have a look. It will probably put you off for life.
Going Indie With An Ebook?