The volume of a cone is increasing at the rate of 28pi cubic units per second. At the instant when the radius of the cone is 3 units, its volume is 12pi cubic units and the radius is increasing at 1/2 unit per second. a. At the instant when the radius of the cone is 3 units, what is the rate of change of the area of its base? b. At the instant when the radius of the cone is 3 units, what is the rate of change of height? c. At the instant when the radius of the cone is 3 units, what is the instantaneous rate of change of the area of its base with respect to its height?