An air-traffic controller views two aircraft on his radar screen. The first is at altitude 850 m, horizontal distance 19.6 km and 27.5° south of west. The second aircraft is at altitude 1100 m, horizontal distance 17.4 km and 22.0° south of west. Find out the distance between the two aircraft? (Put the x-axis west, the y-axis south, and the z-axis vertical.)