please help finding the exact answer

A circle has an initial radius of 50 ft when the radius begins decreasing at the rate of 5 fu/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 it as needed.) Differentiate both sides of the equation with respect to t. dA dt at (Type an exact answer, using it as needed. Type an expression using r as the variable.) The rate of change of the area is |ftz / min. (Type an exact answer in terms of It.) X VI VI More Enter your answer in each of the answer boxes. ? 13