Contextual Applications of Differentiation · Hard problem

Water is poured into an inverted conical tank (height $12$ ft, top radius $6$ ft) at $4$ ft$^3$/min. How fast is the water level rising when the depth is $3$ ft? (Hint: $r=\tfrac{h}{2}$, so $V=\tfrac{\pi h^3}{12}$.) Round to 3 decimal places (an exact answer is also accepted).