Johns paint crew knows from experience that its 18-foot ladder is particularly stable when the distance from the ground to the top of the ladder is 5ft more than the distance from the building to the base o the ladder as shown in the figure. In this position, how far up the building does the ladder reach

A = Height
B = Length
C = Hypotenus

A = X + 5
B = X
C = 18

Plug values into the Quadratic equation.

http://upload.wikimedia.org/math/3/e/a/3ea647783b5121989cd87ca3bb558916.png