A ladder is put against a building. The building is 25 feet tall. The ladder's base is 13.5 feet from the building. Find the angle which the ladder makes with the ground.

Me i've asked this question 3 time asapright triangle abc and its image, triangle a'b'c' are shown below. algebraically prove that a clockwise and counterclockwise rotation of 180o about the origin for triangle abc are equivalent rotations.