Answer:
3 s
Explanation:
Using this quadratic, max height will occur at t = -b/2a
t = - 48 / (2*-16) = 1.5 seconds to max height
then another 1.5 seconds to fall to the ground
for a total of 3 seconds.
Another way d = 0 when it hits the ground
0 = -16 t^2 + 48 t + 0
0 = - 16t ( t +3 ) again shows t = 3s (or 0 before it is launched)