A watermelon is assumed to be spherical in shape while it is growing. Its mass, M kg, and radius, r cm, are related by the formula M = kr3 , where k is a consta

A watermelon is assumed to be spherical in shape while it is growing. Its mass, M kg, and radius,

r cm, are related by the formula M = kr3

, where k is a constant. It is also assumed that the radius is

increasing at a constant rate of 0.1 centimetres per day. On a particular day the radius is 10 cm and

the mass is 3.2 kg. Find the value of k and the rate at which the mass is increasing on this day.