The radius r of a sphere is increasing at a rate of 9 inches per minute. We will find the rate of change of the volume V of the sphere when r = 10 inches and when r = 26 inches. An equation involving V and ris V-4/3m. Differentiate this equation with respect to time to obtain a formula for dV/dt in terms of rand dr/dt: dV/dt = 9 cubic inches per minute Now use what you know about dr/dt to compute dV/dt when r = 10: When 10, dv/dt = cubic inches per minute Now use what you know about dr/dt to compute dV/dt when r = 26: When r = 26, dv/dt = cubic inches per minute