Answer
1. Corresponding parts of parallelograms are congruent.
2. Thus, angle Q is congruent to angle N, PN is congruent to MQ, and QS is congruent to TN.
3. Thus, by SAS, triangle QMS is congruent to triangle NPT.
4. Since CPCTC, this means that opposite sides of MSPT are congruent.
5. By definition, this means that MSPT is a parallelogram.