ANSWER and EXPLANATION
We are given triangles PQS and RSQ.
We need to prove that they are congruent.
Congruent triangles are triangles that have the same length of sides and same angles.
We are given that PQ is equal to RS.
So one pair of sides is equal.
We see that the two triangles share a side.
This means that two pair of sides of the traingles are equal.
Since we are given that according to the SAS (side angle side) postulate, the two triangles are equal.
Note: SAS states that if two triangles have two sets of equal side and a pair of equal angles, they are congruent.