A 20 ft ladder is leaning up against a wall. The wall forms a 90 degree angle with the floor, which has recently been waxed and is very slippery. The base of the ladder begins to slide away from the wall causing the top of the ladder to slide down the wall toward the floor. When the base of the ladder slides to 12 ft away from the wall, the base is moving at a rate of 1 ft/sec away from the wall. How quickly is the top of the ladder moving toward the floor at that moment?