Answer:
Side Side Angle (SSA) congruence.
Step-by-step explanation:
1) Retrieving the missing data:


Check the triangles below:
2) Side Angle Side congruence tells us that a pair of triangles are congruent if and only if their respective side, angle and side are congruent. Since RS ≅ XY and ST≅YZ and in addition to this, ∠S≅∠Y then the it's SSA postulate.
So, it's SSA.