check the picture below.
so, the height of the cylinder, will be a dimension of the square, and its radius, is also a dimension of the square, since the square is being rotated about to make it.
[tex]\bf \textit{volume of a cylinder}\\\\
V=\pi r^2 h\quad
\begin{cases}
r=radius\\
h=height\\
-----\\
r=7\\
h=7
\end{cases}\implies V=\pi \cdot 7^2\cdot 7[/tex]
