[tex]\bf \textit{area of a circular ring}\\\\
A=\pi (R^2-r^2)\qquad
\begin{cases}
R=\textit{larger radius}\\
r=\textit{smaller radius}\\
--------\\
R=12\\
r=9
\end{cases}\implies A=\pi (144-81)[/tex]
volume of the hollow cylinder, the product of the area of the ring and the height of the cylinder
