f(x) = g(g(x)) - g(x) Plug in 3 for x .
f(3) = g(g(3)) - g(3)
g(x) = 2x - 1 Now let's find g(3) . Plug in 3 for x .
g(3) = 2(3) - 1
g(3) = 6 - 1
g(3) = 5
f(3) = g(g(3)) - g(3) Substitute 5 in for g(3) .
f(3) = g(5) - 5
g(x) = 2x - 1 Now let's find g(5) . Plug in 5 for x .
g(5) = 2(5) - 1
g(5) = 10 - 1
g(5) = 9
f(3) = g(5) - 5 Substitute 9 in for g(5) .
f(3) = 9 - 5
f(3) = 4