A circle has an initial radius of 50 it when the radius begins decreasing at the rate of 5 ft/min. What is the rate in the change of area at the instant that the radius is 14 ft? Write an equation relating the area of a circle, A, and the radius of the circle, r. (Type an exact answer, using x as needed.) Differentiate both sides of the equation with respect to t. dA (Type an exact answer, using x as needed. Typo an expression using r as the variable.] The rate of change of the area is 1 / min. (Type an exact answer in terms of n.)