Quadratic equation

Question

 if someone throws a ball down from a height of 100 meters, the ball's distance from the ground can be modeled by the equation:  where t is the time in seconds and d is the distance in meters.

Answer 1

And the question is ........?????

Typically, it is how long does it take to hit the ground, hence where d=0

0 = 9.8t^2 + 15t - 100

0 = 98t^2 +150t - 1000

Per quadratic formula, one solution is about -4 and disqualified because it is negative.

The other good solution is 2.519473184249