Answer:
See below.
Explanation:
m<PTQ + m<QTR = 180 Angles forming a linear pair sum to 180
m<QTR + m<RTS = 180 Angles forming a linear pair sum to 180
m<PTQ + m<QTR = m<QTR + m<RTS Substitution Property of Equality
m<PTQ = m<RTS Subtraction Property of Equality