f(x)=X^3, f(a+h)-f(a)/h

please help im so lost

thanks

(a+h)^3 = a^3 + 3a^2h + ah^2 + h^3)

so [f(a+h) - f(a)]/h
= [a^3 + 3a^2h + 3ah^2 + h^3 - a^3]/h
= 3a^2 + 3ah + h^2