Answer is C.
For every option, sub in the value and find the answer that matches the equation!
Example for option A, F(x) = x + 4 and G(x) = x²
G(F(x)) = G(x + 4) ーー> sub in the value of F(x)
Let's take the subbed in value, (x + 4) as x, and this x will be the x for G(x).
∴ Since G(x) is x²
G(x + 4) = (x + 4)² ーー> remember (x + 4) is represented as x.
= x² + 16
∴ You know that the answer is not A, do this for all options and you'll find the answer, C!