Here's the question you clicked on:
douglas12
If a baseball is dropped from a helicopter 625 feet above ground, then its distance in feet form the ground t seconds later is modeled by -16t^2+625. How long after the ball is dropped will it hit the ground? A. 1.56 seconds B. 6.25 seconds C. 9 seconds D. 39.06 seconds
They are really asking \[-16t^{2}+625=0\].
So how do you solve it then?
As you would any other quadratic equation. You'll get two solutions. A negative and a positive. You'll take the positive solution because time is positive.