A company designed and sells an ultrasonic​ receiver, which detects sounds unable to be heard by the human ear. The receiver can detect mechanical and electrical sounds such as leaking​ gases, air,​ corona, and motor friction noises. It can also be used to hear​ bats, insects, and even beading water. The receiver is 2121 in. deep. The focus is 7 in.7 in. from the vertex. Find the diameter of the outside edge of the receiver.