If f(x)=g(g(x))-g(x) and g(x)=2x-7, find f(3).

f(3) = g(g(3)) - g(3)

 

g(3) = 2*3 - 7 = -1

 

g(g(3)) = g(-1) = -2 - 7 = -9

 

f(3) = -9 - (-1) = -8