Question

Confused. Diagram b. I cannot figure out what W equals.

Answer 1

I forgot what the theorem is called... maybe corresponding angles? Or parallel lines... But anyways it's angle should add up with 72 to make a straight line at 180 degrees. So it should be 108º

Answer 2

when you see two parallel lines (marked with the double arrows) and a line connecting them, think "transversal"
http://www.mathsisfun.com/geometry/parallel-lines.html

corresponding angles are equal, alternate interior angles are equal,
vertical angles are equal... and two angles that from a straight line add up to 180.

In your case, the two angles add up to 180.