quadratic formula/completing the square?

First off I this is for a review for my class due tomorrow. I lost my notes and I am completely lost. I don't know if this is algebra or not, there used to be a help-board I see that is gone which is a shame (or maybe I'm blind?).

A rock is thrown into the air from a bridge and falls to the water below. The height of the ball, *h* metres, relative to the water *t* seconds after being thrown is given by:

h(t)=-5t2+10t+35

a) Determine the maximum height of the rock above the water.

b) How long does it take the rock to reach the maximum height?

c) After how many seconds does the rock hit the water?

Thanks in advance, I really hate exam time, so stressful. :P