If the radius of a sphere is increasing at a constant rate of 2 $\rm{cm}/\rm{sec}$, then the volume is increasing at a rate of $\rm{cm}^3/\rm{sec}$ when the radius is 3 $\rm{cm}$.

Hint: $\displaystyle\frac{dV}{dt} = \frac{dV}{dr} \cdot \frac{dr}{dt}$, and the volume of a sphere is $V = \frac{4}{3} \pi r^3$.