Answer:
Explanation:
If the projectile is hitting something on the ground, it has a height of 0. Sub in a 0 for the h and factor to solve for t:

Factor out a -16t to get
0 = -16t(t - 2.5) which means that either t = 0 or t = 2.5
I'd say it has to be t = 2.5, don't you? ; )