Your physics class decides to perform an experiment on circular waves. First, you make sure the water in the school swimming pool is level; that is, there are no waves. Next, a volunteer tosses a small marble near the center of the pool. Your teacher tells you the radius (in feet) of the outer ripple is given by r (t) = 0.73t, where t is the time in seconds after the marble hits the water given. The area of the circle is given by the function A(r) = π r2, where A(r) is the area in square feet and r is the radius in feet.