A ball is thrown vertically upward from the ledge of a building 75 feet above ground. The ball s height h in feet above the ground at time t in seconds is given by the equation
(a) how long does it take the ball to reach a height of 90 feet?
(b) How long before the ball is back to its original position (at 75 feet)?
(c) How long before the ball hits the ground? Give each answer to the nearest one-thousandth of a second.