The radius $\displaystyle r$ of a right circular cone is increasing at a rate of 2 inches per minute. The height $\displaystyle h$ of the cone is related to the radius by $\displaystyle h=3r$. Find the rates of change of the volume when :

$\displaystyle r$ = 6 inches

and

$\displaystyle r$ = 24 inches

How can I set up the derivative and solve down? (step by step instruction works best for me )