Question 407925
h=-16t^2+128t+144
.
h is height from the ground.
To find your answer set h to zero and solve for t:
0=-16t^2+128t+144
dividing both sides by -16:
0 = t^2+8t-9
factoring the right:
0 = (t-9)(t+1)
t = {-1, 9}
throw out the negative solution leaving:
t = 9 seconds