Depends on how quick and steadily the author writes.
I.E. Kingsley Amis wrote exactly 500 words every morning before starting his day.
How much an author makes depends on sales and his/her contract. If their contract stipulates that s/he receives 15% but only sells $10,000 worth of books, obviously s/he won't receive much.
If s/he has the same contract but sells $10 million in books, then they receive more money.
It's usually based on percentages not on a precise number, excluding advances.