This is function composition, so:
[tex]\begin{gathered} f(x)=x^2,g(x)=\sqrt[]{7-x}\text{ } \\ (f\circ g)(x)=f(g(x))=g(x)^2=(\sqrt[]{7-x})^2 \\ (f\circ g)(x)=(\sqrt[]{7-x})^2 \end{gathered}[/tex]
And (f o g)(0) is:
[tex]\begin{gathered} (f\circ g)(0)=(\sqrt[]{7-0})^2 \\ (f\circ g)(0)=(\sqrt[]{7})^2=7^{} \end{gathered}[/tex]
The answer is (f o g)(0) = 7
