Okay so what you are looking at is a triangle with a cross section. That is line segment PQ.You ae asked to find the length of PN. What you are given is the height(s) of NQ (5 units), QM (2 units) and PL (3 units). You can make an educated guess that line NP equals 4 units. Mainly because those two little arrows on lines LM and PQ (that means that the two lines are parallel). hope it helps...
