The question states: Someone throws a ball straight down to to the floor. If the ball bounces straight up and returns to the floor 2.5s after first striking it, what was the ball's greatest height above the floor?

I have no idea how to go about answering this question. If anyone can help, that would be great. ;)

Neglecting air friction, the ball travels upwards for the same amount of time that it travels downwards. Total travel time is 2.5s, so that means it goes up for 1.25s (max velocity zero height to zero velocity max height) and down for 1.25s (zero velocity max height to max velocity zero height).

So, now you have a ball that starts at zero velocity, and accelerates at a constant acceleration for 1.25s, and you need to find out how far it travels. I'm sure you have a formula for that somewhere.. . ;)