There are three possible answers:
Angle YXZ
Angle ZXY
Angle X
===========================================
Step-by-step explanation:
The idea is that the vertex of the angle is always in the middle of the three letter sequence. You can start with either side which is why ZXY is the same as YXZ. As long as X is in the middle, we're talking about the same angle. Because there are only three points here, and no other points to cause confusion, this means that "angle YXZ" can be shortened to "angle X" to make things easier.