A ball is kicked off a pier & lands in the sea. h(t)=2/7(t+3)(7-t) h=height, t = secs. When does the ball land in the sea?

h = (2/7)(t + 3)(7 - t)

When h = 0 :
(2/7)(t + 3)(7 - t) = 0
(t + 3)(7 - t) = 0
t = -3 (rejected) or t = 7

The ball lands in the sea in 7 seconds.

Max height = dh/dt=0
2/7 ((7-t) -(t+3))=0
This gives
4=2t,
t=2, This much time to come down. That will 4 seconds.

I'll assume that the height is measured above sea level not the level of the pier. If so we simply want the time 't' when the height is zero:

0 = 2/7(t+3)(7-t). Now just look at this equation; the only positive value for t that evaluates correctly is t = 7.

what type of ball? different balls travel at different velocities.