A spherical party balloon is being inflated with helium pump

A spherical party balloon is being inflated with helium pumped in at a rate of 9 cubic feet per minute. How fast is the radius growing at the instant when the radius has reached 1 ft? (The volume of a sphere of radius r is V = 4/3(pi(radius))^3

Solution

V = 4/3*pi*(r)^3 dV=4*pi*(r)^2*dr given dV=9 r=1 9=4*3.14*1*dr dr=0.7165