I have no idea how to start this, I know that $\displaystyle V = \frac{1}{3} \pi r^{2} h $A hallow rigght circular cone has height 18cm and base radius 12cm. It is held vertex downwards beneath a tap leaking at the rate of $\displaystyle 2 cm^{3} s^{-1} $

Find the rate of rise of water level when the depth is 6cm.

any help appreciated,

thanks