21. A ball is thrown downward from a height of 256 feet with a velocity of 60 feet per second. How long will it take for the ball to reach the ground? 22. A rock was dropped from a cliff (the cliff is 150 ft above the ground), and the rock's height above the ground is h(t) 150 - 15t. a) What would have been the rock's velocity and acceleration at time t? b) About how long does it take for the rock to hit the ground? c) What is the rock's velocity at the moment of impact?