Ap Calc Problems

How to solve this problem? (AP CALC)?

the radius of a circle is decreasing at a constant speed of 0.1 inches second. In terms of the circumference C, what is the rate of change of area of a circle, in square centimeters per second?

A = pi r ^ 2 Differentiate with respect to time, A '= 2pi rr' = Cr '= 0.1C, cm ^ 2 / s

AP Calc Teach Me Problem 4