i need help on number 71 and 75 thank you?

71)
f(x) = (5x+4)^(1/3)
g(x) = (1/5)x^3 -4/5

(f.g)(x) = f( g(x) )
= f ( (1/5)x^3 - 4/5)

= (5 ( (1/5)x^3 - 4/5) +4 )^(1/3)
= ( x^3-4+4)^(1/3)
= (x^3)^(1/3)
= x

g( f(x)) = g ( (5x+4)^(1/3) )
= (1/5) ((5x+4)^(1/3))^3 - 4/5
= (1/5) (5x+4) - 4/5
= x + 4/5 - 4/5
= x

75)
f(x) = x^2-4
f(x+h) = (x+h)^2 - 4
f(x+h)= x^2+2xh+h^2 - 4

f(x)+f(h) = x^2-4 + h^2 - 4
= x^2+h^2-8

71) f(x) = ∛(5x + 4) , g(x) = (1/5)x^3 - 4/5

f(g(x)) = ∛[5((1/5)x^3 - 4/5))+ 4] = ∛(x^3 - 4 + 4) = ∛(x^3) = x

g(f(x)) = (1/5) [∛(5x + 4)]^3 - 4/5 = (1/5)(5x + 4) - 4/5 = x + 4/5 - 4/5 = x
▮

75) f(x) = x^2 - 4

f(x + h) = (x + h)^2 - 4 = x^2 + 2xh + h^2 - 4

f(x) + f(h) = x^2 - 4 + h^2 - 4 = x^2 + h^2 - 8

75/
f(x)=x^2-4
f(x+h)=(x+h)^2-4
f(x)+f(h)=x^2-4+h^2-4=...