In the diagram, .

Triangles P M N and Q S R are shown. The lengths of sides P N and R Q are congruent, the lengths of sides Q S and P M are congruent, and the lengths of sides M N and R S are congruent.

If QR = 20 in., RS = 7 in., and SQ = 24 in., what is PN?

3 in.
7 in.
20 in.
24 in.