The bottom of a large theater screen is 6 ft above your eye level and the top of the screen is 20 ft above your eye level. Assume you walk away from the screen {perpendicular to the screen} at a rate of T le while looking at the screen. What is the rate of change of the viewing angle El when you are 70 ft from the wall on which the screen hangs, assuming the oor is at {see gure)