math
posted by anonymous .
a 15 foot ladder is placed against a vertical wall of a building with the bottom of the ladder stand on level ground 12 feet from the base of the building. How high up the wall does the ladder reach?

a^2 + b^2 = c^2
a^2 + 12^2 = 15^2
a^2 + 144 = 225
a^2 = 81
a = 9