Answer: W = 40 degrees.
Step-by-step explanation: When you're finding a missing interior angle, all you need is the angle measurements of the other two angles. According to the picture, we have two 70's given, which both add up to 140. All the interior angles of a triangle need to add up to 180, and we have 140 so far. That's where the missing angle comes in. When you subtract 140 from 180, you get 40, which is your missing angle.
Let me know if this is right! :)