Ans: (a) $3$ (b) $54\text{ cm}^3$
-
$\begin{array}{rcl}
\dfrac{1}{3}\pi r^2(12) & = & 2\times \dfrac{1}{2}\times\dfrac{4}{3}\pi r^3 \\
4 & = & \dfrac{4}{3} r \\
r & = & 3
\end{array}$ - The volume of the solid
$\begin{array}{cl}
= & \dfrac{1}{3} \pi (3)^2 (12) + \dfrac{1}{2}\times\dfrac{4}{3}\pi (3)^3 \\
= & 54\mbox{ cm}^3
\end{array}$
