20500 - ( 20500/100*16)= 20500-3280=17220
17220 - (17220/100*16) = 17220- 2755.20= 14464.80
14464.8 - (14464.8/100*16) = 14464.80 - 2314.37=12147.43
12147.43 - (12147.43/100*16) =12147.43- 1943.59=10203.84
10203.84 -(10203.84/100*16)=10203.84-1632.61= 8571.23
BUT I rounded as I went otherwise it would have taken longer to write but you can add it and by my answer it would be D - you can check it :)