Assume that the radius r of a sphere is expanding at a rate of 40cm/min. The volume of a sphere is = 4 / 3 3 V=4/3pir 3 and its surface area is 4 2 4pir 2 . Determine the rate at which the surface area is changing with respect to time at t = 2 min, assuming that r = 10 at t = 0. (Use symbolic notation and fractions where needed.)