A rescue team is deployed via helicopter to rescue a struggling swimmer. The helicopter locates the swimmer, who is several feet from a tethered buoy. The helicopter hovers 400 feet over the buoy as its team prepares to rescue the swimmer. Initially, the swimmer sees the helicopter at an angle of elevation of x degrees. The swimmer then swims 5 feet closer to the buoy, and now sees the helicopter at an angle of y degrees. Which trigonometric equation correctly models the distance the swimmer swam toward the buoy in terms of x and y?