Steps:
2) QR || TS
3) QT || RS
4) <1 = <4, as they are alternate interior angles between parallels.
5) <2 = <3, as they are alternate interior angles between parallels.
6) RT = RT, by the reflexive property.
7) Triangle QRT = Triangle SRT, by the ASA postulate.
8) QR = ST and QT = RS, as they are corresponding sides of congruent triangles.