Cecily is on her roof and wants to throw a ball straight up in the air and figure out how long it will take to reach the ground. The function that models an object falling to the ground is f(x) = -32x2 + vx + d. In this function, x is time, v is the initial (vertical) velocity in feet per second, and d is the initial distance above the ground in feet. If v is positive, then the initial velocity is upward. If v is negative, the initial velocity is downward.