If f(x)=g(g(x))-g(x) and g(x)=2x+1, find f(3).
g(x) = 2x + 1 ---> g (g(x) ) = 2( 2x + 1 ) + 1 = 4x + 2 + 1 ---> 4x + 3
g( g(x) ) - g(x) = [ 4x + 3 ] - [2x + 1 ] = 4x + 3 - 2x - 1 = 2x + 2
f(3) = 2(3) + 2 = 6 + 2 = 8
