Omg that's easy, a^2 + b^2=c^2. The longest side is your hypotenuse. The shortest side is your A. Basically just plugging it in. After you set it up you unsquare it. Then find the square root of the missing side. This is from my knowledge, so if you're still confused, ask your teacher for clarification, because it took me the second day to get it. Or just watch a video on it.