We are asked to find z = g0f or what is the same:
z = g (f (x))
That is, we must introduce the function f (x) within the function g (x)
So, we have
f (x) = 3x-9
g (x) = x ²
Therefore we have the following function
z = (3x-9) ²
Finally (g0f) (5) = (3 (5) -9) ²
(g0f) (5) = 36
