The radius of a right circular cone is increasing at a rate of 6 inches per second and its height is decreasing at a rate of 5 inches per second. At what rate is the volume of the cone changing when...

 The radius of a right circular cone is increasing at a rate of 6 inches per second and its height is decreasing at a rate of 5 inches per second. At what rate is the volume of the cone changing when the radius is 30 inches and the height is 20 inches?