Some interesting math here from Business2Community.com.
The calculation is as follows:
revenue = books sold on Amazon x book price x 0.225 = 1340 x 35 x 0.225 = $10553
The period tracked is just shy of a whole week, so we can round up to approximately $11 000 per week, or $44 000 per month, or around $484 000 per year (although there will be some serious fluctuations depending on season, reviews, marketing campaigns, and so on).
Who knows how accurate this is, but it kinda makes sense if King really gets just under 23% of each book sold. And of course this is only Amazon's sales numbers.
Check out the whole article here.