Sand is pouring out of a pipe at a rate of 80 cubic feet per hour.

and is forming a conical pile on the ground.

The height is always $\displaystyle \frac{{1}}{{3}}$ of the radius.



When the pile has a radius of 12 feet,

the RADIUS is increasing at a rate of feet per hour.

Write your answer as a decimal numbers rounded to 2 decimal places.