The radius rin inches, of a spherical balloon is related to the volume V by 3V r() = Air is pumped into the balloon so the volume after t seconds is given by V (t) = 18 + 181. a. Find an expression for the composite function (V). To enter #, type pl. To enter a cube root, use a fractional 1/3 exponent type (1/3) a (V ()) = b. What is the exact time in seconds when the radius reaches 12 inches?