We have the following equation:
h (t) = - 16t ^ 2 + 161t + 128
We substitute the value of h (t) = 170:
170 = -16t ^ 2 + 161t + 128
We rewrite the equation:
-16t ^ 2 + 161t + 128 - 170 = 0
-16t ^ 2 + 161t - 42 = 0
We look for the roots of the equation:
t1 = (161/32) + root (23233) / 32
t2 = (161/32) - root (23233) / 32
Answer:
The object is 170 feet off the ground at the following times:
t1 = (161/32) + root (23233) / 32
t2 = (161/32) - root (23233) / 32