Question 344469
h = -16t^2 + 96t + 640
since h is height, set it to zero and solve for t:
0 = -16t^2 + 96t + 640
Dividing both sides by -16:
0 = t^2 - 6t - 40
0 = (t-10)(t+4)
.
t = {-4, 10}
we can toss out the negative solution leaving:
t = 10 seconds