Question

Two aircraft approaching an aircraft carrier are detected by radar. The first aircraft is at a horizontal distance of
34.2 km
in the direction
44.0°
north of east and has an altitude of
2.36 km.
The second aircraft, at half this altitude, is at a horizontal distance of
42.2 km
in the direction
24.0°
north of east. What is the distance separating the two aircraft? Hint: Use a coordinate system with the x axis pointing east, the y axis pointing north, and the z axis in the vertical direction.

Answer 1

use their hint, and then the distance formula, extended to 3 dimensions.

Answer 2

Im am bit confused, why should I extend it to 3 dimensions? I can see it mentions a Z axis but the exercise only mentions 2 aircrafts, I can't seem to find enough information for it.