But his teacher that he needed to measure the height of a building in which his classroom is located he backs away from the building and places a mirror on the ground between him and the wall when he can see the top of the building in the mirror Peter is 2‘9“ away from the mirror and the mirror is 11 feet away from the wall of the building Peter knew his eye level was exactly 5‘6“ off the ground so he was able to calculate the height of the building how tall is the building in feet