a ball is dropped from a height of 784ft. It's height h, in feet, after t seconds is given by h (t) = 784-16tsquared. After how long will the ball reach the ground?

h (t) = - 16t2 + 64

Time to reach ground:

h (t) = 0

-16t2 + 64 = 0

Solve for t, keeping only the positive solution.

Time to fall 36 ft:

Since it is dropped from 64 ft, its height after falling 36 feet is 64-36=28 ft.

28 = - 16t2 + 64

-16t2 + 36 = 0