At time t = 0 a ball is thrown straight up from a height of 48 metres above the ground. After t seconds its height h, in metres, above the ground is given by h = 48 + 16 − 4^2.

a) What are the possible values for t?
b) Calculate the maximum height of the ball above the ground.
c) How long does it take the ball to return to the ground level?
d) Determine at what time the ball is at the height of 28 m.