2.99
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(a). If A is the area of a circle with radius and the circle expands as time passes, find dA/dt in terms of 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 1m/s, how fast is the area of the spill increasing when the radius is 30 m?