PQRS is a parallelogram Given
SR=PQ property of parallelogram
m∠S=m∠Q property of parallelogram
SP=QR property of parallelogram
XP=RY given
SP-XP=QR-RY substitution
SX=QY segment subtraction
ΔSRX is conggruent to ΔQPY SAS theorem (side-angle-side)
XR=YP CPCTC (corresponding parts of congruent triangles are congruent)