The way SkiffMacKinaw did this problem is the way it should be done. There is another way of doing it by extending both arms of <1 until they intersect p and q and solve the triangle hanging from p.
You then find the the angles of the triangle. The vertex angle is the supplement to <1.
This method works but it is not nearly as elegant as the original answer. This is one of the best awarded Brainliests I've seen lately.