Question

A ball is projected upward from the ground. Its distance in feet from the ground in t seconds is given by

s(t) = -16t^(2)+128t
At what will the ball be at 213ft from the ground?

Answer 1

At what will the ball be ... ????? Time ??

set -16t^(2)+128t = 213 and solve
16t^2 - 128t + 213 = 0
you will get two answers, one positive and one negative.
Reject the negative answer.