8. An apple is launched directly upward at 64

feet per second from a platform 80 feet high

The equation for this apple's height h at time

7 seconds after launch is h = - 1612 + 64t + 80.

How long did it take the apple

to reach the ground?

Step-by-step explanation:

First part:

Set h (t) = 73 and solve for t.

-16t2 + 64t + 16 = 73

-16t2 + 64t - 57 = 0

Solve this quadratic equation for t. You should get 2 positive solutions. The lower value is the time to reach 73 on the way up, and the higher value is the time to reach 73 again, on the way down.

Second part:

Set h (t) = 0 and solve the resulting quadratic equation for t. You should get a negative solution (which you can discard), and a positive solution. The latter is your answer.