[tex]\bf \textit{surface area of a sphere}\\\\
SA=4\pi r^2~~
\begin{cases}
r=radius\\[-0.5em]
\hrulefill\\
SA=400\pi \end{cases}\implies 400\pi =4\pi r^2\implies \cfrac{400\pi }{4\pi }=r^2
\\\\\\
100=r^2\implies \sqrt{100}=r\implies \boxed{10=r}
\\\\[-0.35em]
\rule{34em}{0.25pt}\\\\
\textit{volume of a sphere}\\\\
V=\cfrac{4\pi r^3}{3}~\hspace{7em}V=\cfrac{4\pi \boxed{10}^3}{3}\implies V=\cfrac{4000\pi }{3}[/tex]
