How far from the base of the house do you need to place a 15' ladder so that its exactly reaches the top of a 12' wall?

Sketching the ladder and wall might help to make the question clearer.  The ladder is represented by the hypotenuse of a right triangle and is opposite the 90-degree angle of this triangle.  The opposite side of this triangle measures 12 feet.  Thus, you have 2 of 3 sides in a right triangle:  a 12-foot opposite side and a 15-foot hypotenuse.  Can you now find the measure of the adjacent side, which is the distance the base of the ladder is located away from the base of the wall?  The Pythagorean Theorem would be the easiest approach to use here, but you could also solve this problem using trig.