Ignore the ray that angles 2 and 3 are adjacent to. It might help to copy the drawing but erase that ray in question. All we really care about is the X shape the two lines form along with angles 1 and 4. These two angles are opposite one another. We consider them vertical angles. They don't have to align vertically. They simply have to be opposite one another like this in this X configuration. Vertical angles are always congruent to one another.
