To prove that fghj is a parallelogram which theorem or postulate has to be used first to prove to fhj is congruent to hfg

ASA is the Theorem or Postulate that verifies that fghj is a parallelogram by proving that fhj is congruent to hfg. ASA condition is only satisfied if the 2 angles and 1 side is included in the Triangle. Two opposite adjacent angle are visible upon having the parallelogram a diagonal on it.