Let us recall parallelogram properties, which states that opposite angles of parallelogram are congruent.
We can see from graph that side US is parallel to TR and measure of angle U equals to measure of angle R, therefore, quadrilateral drawn in our given graph is a parallelogram.
Since we know that opposite sides of parallelogram are congruent. In our parallelogram UT=SR and US=TR.
In our triangle STU and triangle TSR side TS=TS by reflexive property of congruence.
Therefore, our triangles are congruent by SSS congruence.
