When the ball reaches the ground, its height is 0.
We set the height function equal to zero and solve for t, the time.
h = -16t^2 + 250
-16t^2 + 250 = 0
16t^2 - 250 = 0
or 
or 
or 
We discard the negative solution since time must be positive.
The positive solution is
Answer: 4.0 seconds
We set the height function equal to zero and solve for t, the time.
h = -16t^2 + 250
-16t^2 + 250 = 0
16t^2 - 250 = 0
We discard the negative solution since time must be positive.
The positive solution is
Answer: 4.0 seconds