$h = \dfrac{4}{3}r$
$\dfrac{dh}{dt} = \dfrac{4}{3} \cdot \dfrac{dr}{dt}$
$\dfrac{dh}{dt} = \dfrac{4}{3} \cdot \dfrac{3}{12}$
$\dfrac{dh}{dt} = \dfrac{1}{3} ~ \text{ft/min}$
$Q = vA$
$\dfrac{dV}{dt} = \dfrac{1}{3} \cdot \pi(3^2)$
$\dfrac{dV}{dt} = 3\pi ~\text{ft/min}$ ← answer
