h is the height at time t
t is the time
v is initial vertical velocity
s is initial height
s = 68ft, v = 128ft/s
Therefore
h = -16t^2 + 128t + 68
The time the ball is in the air is the time it took the bullet to hit the ground (h = 0)
To find the time taken for the bullet to be in the air,
we set h = 0.
Dividing through by -16, we have;
Since t cannot be negative, then the only possibility is
t = 8.5s
Hence the bullet was in the air for 8.5s