36,120 was the original cash prize
let's put this in an equation ->
[tex] \frac{29}{100} [/tex] = [tex] \frac{28,000}{y} [/tex]
a clever way to figure out y, which here would be the original cash prize, is as follows:
28,000 ÷ 100 = 280
280 × 29 = 8120 (this is the tax he paid)
now, add the tax to what he recieved -> 28000 + 8120 = 36120