18. Using vertical angle theorem, 1 is equal to 2 and 3 is equal to 4. Therefore 2 is equal to 40 degrees. Then since 2 and 3 are supplementary adjacent angles or a linear pair, they equal 180 when combined. 180-40 equals 140. 3 and 4 are also vertical angles so 3 = 4 and they are both 140.
19. Angles 1 & 3 and 2 & 4 are vertical angles because they are directly across from each other and share the same bisectors. You can use what you know about special angle pairs to find the measure of each angle because since 1 & 3 are vertical angles and 2 & 4 are also vertical angles, 1 is equal to 3 and 2 is equal to 4. So, since the angle formed at the right is angle 2, we can confirm that angle 4 is equal to it and therefore angles 2 and 4 are 46 degrees. Then since angles 1 & 2 and 3 & 4 are linear pairs, we can say that angle 1 + angle 2 is equal to 180 and the same for angles 3 & 4. So subtract 180 - 46 and you get 134. Therefore angles 1 and 3 are equal to 134 degrees.
