The answer is D. Think about this question for a minute: We're told that a 25 foot ladder is placed against a building that is perpendicular to level ground and that the bottom of the ladder is 7 feet away from the base of the builiding. Automatically, one should realize that this is a pythagorean theorem problem since we have a right triangle with the hypotenuse being 25 and one of the legs being 7. The other leg is the height of the building and can be found by doing: sqrt(25^2-7^2)=24.
Later on, the problems asks us how many feet farther away from the building will the bottom of the ladder be when its height is decreased by 4. This is another pythagorean theorem problem. Since the orig. height is supposed to be decreased by 4, we do 24-4=20 and the hypotenuse of the ladder is still the same (25). So to find the distance from the bottom of the ladder to the base of the building: We do sqrt(25^2-20^2)=15
The window washer must move the ladder 15-7=8 feet farther from the base of the building if he wants the height top of the ladder to be 4 feet lower.
