To prove that triangles TRS and SUT are congruent we can follow these statements:
1.- SR is perpendicular to RT: Given
2.-TU is perpendicular to US: Given
3.-Angle STR is congruent with angle TSU: Given.
4.-Reflexive property over ST: ST is congruent with itself (ST = ST)
From here, we can see that both triangles TRS and SUT have one angle of 90 degrees, another angle that they both have, and also they share one side (ST) ,then:
5.- By the ASA postulate (angle side angle), triangles TRS and SUT are congruent