Explanation:
Since L is the midpoint of JM, then JL = LM.
Therefore,
Statement: JL = LM
Reason: L is the midpoint of JM
The lines JK and NM are parrallel; therefore, by the alternate interior angles theorem,

Furthermore, since ∠JLK and ∠MLN are vertical angles,

Now since ∠JLK = ∠MLN, ∠LJK = ∠LMN, and JL = LM, then by ASA postulate

Hence, our proof is complete!