ok so this problem seems pretty straight forward.

a ball is thrown straight up from the ground with an initial velocity of 256 ft/s. the equation h = 256t -16t^2 describes the height the ball can reach in t seconds.

ok so i take the first derivative and find that t = 8 seconds or in 8 seconds the ball reaches the max height.

when i plugged in the 8 seconds i got 1024 as the max height in feet, my book says the answer is wrong? ok so where did i mess up?