(a) If $A$ is the area of a circle with radius $r$ and the circle expands as time passes, find $dA/dt$ in terms of $dr/dt$. Below, use "s" for $dr/dt$.

(b) Suppose oil spills from a ruptured tanker and spreads in a circular pattern. If the radius of the oil spill increases at a constant rate of $1 m/s$, how fast must the area of the spill increasing when the radius is $22 m$?

(a) $dA/dt =$
(b) $dA/dt =$ $m/s^2$