The radius r, in inches, of a spherical balloon is related to the volume I by 3V r (V) = Air is pumped into the balloon so the volume after t seconds is given by V (t) = 12 + 16t. a. Find an expression for the composite function r (V (t)). To enter it, type pi. To enter a cube root, use a fractional 1/3 exponent, type "(1/3)". r (V (t) ) = b. What is the exact time in seconds when the radius reaches 16 inches? t