Step-by-step explanation:
0 = -x² + 2x + 3
0 = x² − 2x − 3
0 = (x − 3) (x + 1)
x = -1 or 3
These represent the times that the ball's height is 0. Since negative time doesn't make sense in this context, we would ignore it and say that the ball lands after 3 seconds.
