Just for fun, two 150 lb engineering students A and B intend to jump off the bridge (120 feet above the horizon) from rest using an elastic cord (bungee cord) having a stiffness k = 75 lb/ft. They wish to just reach teh surface of the river, when A, attached to the cord, will let go of B at the instant they touch the water. Determine the proper unstretched length of the cord to do the stunt.