ILL 1976 Problem 15

Let $ABC$ and $A'B'C'$ be any two coplanar triangles. Let $L$ be a point such that $AL || BC, A'L || B'C'$ , and $M,N$ similarly defined. The line $BC$ meets $B'C'$ at $P$ , and similarly defined are $Q$ and $R$ . Prove that $PL, QM, RN$ are concurrent.