21. Allison kicks a stone off the edge of a tall cliff. The distance d (in feet), between the rock and the ground / seconds after being kicked is d(t)= +41 +474. [4 points] a. How many seconds elapse before the rock is at a height of 424 feet above the ground? Round your answer to the nearest tenth of a second. [2 points] b. What is the maximum height that the rock reaches? Round your answer to the nearest whole foot. [2 points]