Exercise 17 Page 631

The given information tells us that M is the midpoint of NL. By the definition of a midpoint we can therefore say that NM≅ ML. Let's add this information to the diagram.

Also, we know that QM and PL are parallel lines. If we view NL as a transversal to these parallel lines, we can say by the Corresponding Angles Theorem that ∠ QMN and ∠ PLM are congruent.

Now we have enough information to claim the triangle are congruent by the ASA Congruence Theorem.