PLEASE GUYS I NEED THIS ANSWER!! (Trolls and links will get reported)

X+ y = 5 ; x - y =3 solve using linear combination

Hey free points ! people i have a few math questions on my profile consider looking at them i have to get done in 30 mins!

(fog)(x) if f(x)=x^2- 4 and g(x)=x^2 + 2 x, f(g(x))= f(x^2+2x) (x^2+2x)^2-4 (x^2+2x)(x^2+2x)-4 (x^4+2x^3+5x+4x^2)-4 x^4+2x^3+4x^2+5x-4 what am i doing wrong