The height of a ball in feet is modeled by y 16x2 72x wher

The height of a ball in feet is modeled by y = -16x^2 + 72x, where x is the time in seconds after the ball is hit. How long is the ball in the air?

a. 2.25s

b. 4.5s

c. 9s

d. 81s

I chose answer b, 4.5 seconds. Is that right?

Yes the answer is correct 4.5s

you just have to solve the quadratic equation 16x2+72 = 0

solving which you get x = 0 and x = 4.5

so at 4.5 seconds the ball comes back and hits the ground