Thaat's > 7
10^9 dollars to developers. So how many devs are out there? if we assume [for no good reason] 100,000 (10^5) devs that's 710^9/10^5 = 7*10^4 (70,000) dollars per dev. Adjust the number of devss to suit your prejudices.
This does not include devs who are hired by banks, stores, etc. which give their apps to customers for free.