I don't understand this problem at all. Can someone please help me break it down? I would post my work if I even knew how to start it but I don't.

Sand falls from a conveyor belt onto the top of a conical pile at a constant rate of 15 m^3/min. The height of the pile is always 3/5 of the base diameter. How fast is the height changing when the pile is 3 m high? At the same instant, how fast is the base radius changing?