Dont remember how to solve h(t) = -16t^2 + 64?

At the water, h(t)=0, because it's zero feet of the ground/water. This means you have 0=-16t^2+64. Add 16t^2 to each side ( 16t^2=64 ), divide by 16 ( t^2=4 ) and take the square root ( t=2 ). This means he'll take two seconds to hit the water, or, more exactly, he will be at the water level at two seconds. Remember that you don't take the negative squarer root because you don't travel back in time!