hint:
[tex]\bf \textit{volume of a cylinder}\\\\
V=\pi r^2 h\qquad
\begin{cases}
r=radius\\
h=height\\
--------\\
\textit{double the "h"}\\
h=2h
\end{cases}\implies
\begin{array}{llll}
V=\pi r^2 (2h)\\\\
V=2\pi r^2 h\\\\
V=2(\pi r^2 h)
\end{array}[/tex]
