An air-traffic controller notices two aircraft on his radar screen. The first is at altitude 850 m, horizontal distance 19.6 km, and 27.0° south of west. The second aircraft is at altitude 1100 m, horizontal distance 17.4 km, and 18.0° south of west. What is the distance between the two aircraft? (Place the x axis west, the y axis south, and the z axis vertical.)