**maximum height is reached at 4 seconds**.

This the vertex of the parabola and is halfway on the trajectory, so **at t=8, h=0, when it reaches the ground**. You can also see this from the original equation h=-16t²+128t=16t(-t+8) when t=8, h=0. Of course, when t=0, h=0 at the start of the trajectory.

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