Question 665167
-{{{P}}}--------{{{Q}}}-------{{{R}}}---------{{{S}}}-

1. {{{PQ = RS}}}.............................Given
2. {{{PQ + QR = QR + RS}}}...................Addition Postulate
3. 
{{{PQ + QR = PR}}}; 
{{{QR + RS = QS}}}..........Segment Addition
4. {{{PR = QS}}}.............................Substitution)