The composition
[tex](f\circ g)(x)[/tex]Means that you have to evaluate x in g(x) first, and then evaluate that result in f(x)
In other words:
[tex](f\circ g)(x)=f(g(x))[/tex]Let's use this for this question:
[tex]\begin{gathered} f(x)=(x+1)^3 \\ g(x)=\sqrt[3]{x}+1 \\ \\ (f\circ g)(-64)=f(g(-64)) \\ \rightarrow g(-64)=-3 \\ \rightarrow f(-3)=-8 \\ \\ \text{Thereby} \\ (f\circ g)(-64)=-8 \end{gathered}[/tex]