Differentiation

The area of a circle is decreasing at \(12\pi\text{ cm}^2\text{ s}^{-1}\).
When its radius is \(3\text{ cm}\), find:

1. the rate of change of its radius;

2. the rate of change of its circumference.

Use \(A=\pi r^2\) and \(C=2\pi r\).