The equation represents height as a function of time.
The bullet was in the air for 75 seconds.
The equation is given as:

The time spent in the air is the time it takes the bullet to land on the ground.
When the bullet is on the ground, the height is:

So, we have:


Factor out t

Split
or 
represents when the shot is fired.
So, we solve for t in 
Collect like terms

Divide both sides by 16

Hence, the bullet was in the air for 75 seconds
Read more about height and time at:
brainly.com/question/2261757