vertical motion, zero velocity practice problems

Question

a cereal box falls off of a 9-foot shelf. the function h=-16t^2+9 gives the height (in feet) of the box after t seconds. how many seconds does it take for the box to hit the floor?

Answer 1

-16t^2 +9 = 0

t^2 = 9/16

t = sqr(9/16) = 3/4 second = 0.75 second to reach the ground