The radius of a circular puddle is growing at a rate of20cm/sec.(a) How fast is its area growing at the instant when the radius is40centimeters? HINT [See Example 1.] (Round your answer to the nearest integer.)

cm²/s

(b) How fast is the area growing at the instant when it equals16square centimeters? HINT [Use the area formula to determine the radius at that instant.] (Round your answer to the nearest integer.)

cm²/s