You can solve this problem by following the steps below:
 1. You need the formula for calculate the area of a circle, which is:
 A=πr²
 "A" is the area of the circle
 "r" is the radius of the circle (r=35 centimeters).
 2. Now, you must take the derivative. Then, the rate of change of the area is:
 dA/dt=(2πr)(dr/dt)
 3. The radius of change of the radius "r" with respect to time, is:
 dr/dt=6 cm/min
 4. Then, you have:
 dA/dt=(2πr)(dr/dt)
 dA/dt=2π(35 cm)(6 cm/min)
 dA/dt=420π cm²/min