Sand is poured onto a surface at 15 cm^3/ sec, forming a conical pile whose base diameter is always equal to its altitude. How fast is the altitude

Sand is poured onto a surface at 15 cm^3/ sec, forming a conical pile whose base diameter is always equal to its altitude. How fast is the altitude of the pile increasing when the pile is 1 cm high? Note that the volume of a cone is (1/3)πr^2h where r is the radius of the base and h is the height of the cone.