A 20ft ladder leans against a house. The bottom of the ladder is 8 feet from the base of the house. To the nearest foot, how high above the ground is the top of the ladder?

Actually, you need to use the Pythagorean Theorem for this problem. Set it up like

${8}^(2) * {x}^(2) = {20}^(2)$
then solve for x to find the height

Should come out to be around 18 feet