A spherical balloon is being inflated. Find the rate of increase of the surface area ($S=4\pi r^2$) with respect to the radius $r$ when $r$ is:
(a) 1 ft
(b) 2 ft
(c) 3 ft
(What can you conclude?)

Note: Please leave all your answers in terms of "pi".

(a) sq cm/sec
(b) sq cm/sec
(c) sq cm/sec