the cylinder is not a right-circular cylinder, is rather a slanted cylinder, however, recall Cavalieri's Principle, if the cross-sections of the slanted cylinder are the same as the cross-sections of a right-cylinder at each height, then their volume is the same.
so the volume of this slanted cylinder is really the same volume as a right-circular one,
[tex]\bf \textit{volume of a right-circular cylinder}\\\\
V=\pi r^2 h~~
\begin{cases}
r=radius\\
h=height\\
-----\\
r=3\\
h=6
\end{cases}\implies V=\pi (3)^2(6)\implies V=54\pi [/tex]
