Noah wants to take a picture of a beach front. He wants to make sure two palm trees located at points A and B are just inside the edges of the photograph. He walks out on a walkway that goes over the ocean to get the shot. Point A is 90 feet from the entrance of the walkway, and point B is 40 feet from the entrance. If the walkway is perpendicular to AB, and Noah’s camera has a viewing angle of 90°, at what distance down the walkway should Noah stop to take his photograph?