A ball is thrown downward with a speed of 8 ft/s from the top of a 68 ft tall building. After t seconds, its height above the ground is given by s(t)=-16²-8t+ 68. a 68 ft ta (a) Determine how long (in s) it takes for the ball to hit the ground, 1.82666 x (b) Determine the velocity (in ft/s) of the ball when it hits the ground. 66.453 ttu/s