[tex]\bf \textit{volume of a cylinder}\\\\
V=\pi r^2 h~~
\begin{cases}
r=radius\\
h=height\\
------\\
r=8.2\\
h=3
\end{cases}\implies V=\pi 8.2^2(3)\implies V=201.72\pi[/tex]
whatever% of anything is just (whatever/100) * anything.
thus, 81.7% of V is just (81.7/100) * V.