Since vertical angles are equal you can put the same value to the opposite angles. Also, you were given a supplementary angle which are two angles added to 180 degrees. Of those 180 you were given 100. The angle next to the 100 degrees has a value of 80. With all this, you add all the angles together and put it equal to 180 which is what the angles of a triangle add up to. Then you combine like terms to get the value of X and just replace it for x. After that you just multiply and then add.
