You and a group of friends are participating in a ropes course. One of the obstacles involves doing a Tarzan Swing into a lake. A rope swing is at the edge of the lake. It is attached to a platform arm that overhangs the lake as shown in the diagram below. The point at which the rope is attached is 30 feet above the water and 20 feet from the bank. The platform is on the 20-foot bank at the edge of the lake and is 20 feet high. The rope is 35 feet long, allowing the rope to hang down in the water so that a swimmer can reach it and tow it back to shore or the next group member. The rope is knotted every five feet so that swingers have something to hold as they swing out over the lake. How long is the part of the rope that is stretched from the attachment point to the edge of the bank?