Supplementary angles are angles that add up to 180 degrees. We can see in the picture that both angles are located on the same line, and no other angles are involved, so they must equal 180.
We can also use the process of elimination:
∡RSQ and ∡UVS are congruent because they are consecutive angles.
∡RSQ and ∡WVX are also congruent because they are alternate exterior angles.
∡RSQ and ∡TSV are also congruent because they are vertical angles.
