how di find the answer to my question

f(x) = x^2 + x

g(x) = x-8

f(g(x)) simply means that we replace whatever we see for x [in f(x)] with g(x).

This means that we have g(x)^2 + g(x)

but g(x) = x-8.

(x-8)^2 + (x-8)

FOIL : (x-8)(x-8) = x^2 - 16x + 64

x^2 -16x + 64 + x - 8

x^2 -15x + 56 <---- ANSWER

Hope this helps!