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. dA dr dt 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, ow fast is the area of the spill increasing when the radius is 21 m? m2/s