If Bill throws a apple into the air and the ball follows a p

If Bill throws a apple into the air, and the ball follows a path of the algebraic equation h=-8t^2+40t and H is for height and t for time, how many seconds will it take the for the apple to fall to the ground. have no clue how to even start this

Solution

h(t) = 40t - 8t^2
on the ground, h(t) = 0
40t - 8t^2 = 0
5t - t^2 = 0
t*(5 - t) = 0
t = 0 (at the start)
t = 5 (impact)