Find the value(s) of the variable (s).

13. 5y + 10 = 6y - 2vertical angles are equal
      5y - 6y = -2 - 10
      -y = - 12
       y = 12 <==

     2x + 40 = 110...vertical angles are equal
     2x = 110 - 40
     2x = 70
      x = 70/2
      x = 35 <==

14. x = 0.5x + 17.5vertical angles are equal
      x - 0.5x = 17.5
      0.5x = 17.5
      x = 17.5 / 0.5
      x = 35 <==

      y = 145 <== vertical angles are congruent

15. x + 42 = 52
      x = 52 - 42
      x = 10 <==

     6y + 8 = 7y - 12
    6y - 7y = -12 - 8
          - y = -20
            y = 20 <==

16. 75 + 4y + 25 = 180supplementary angles = 180
      4y + 100 = 180
      4y = 180 - 100
      4y = 80
        y = 80/4
        y = 20 <==

       75 + 2x - 5 = 180...supplementary angles = 180
       2x + 70 = 180
       2x = 180 - 70
       2x = 110
         x = 110/2
         x = 55 <==

17. 3y + 13 + 5y - 1 = 180...supplementary angles = 180
     8y + 12 = 180
    8y = 180 - 12
    8y = 168
      y = 168/8
      y = 21 <==

    11x + 16 + 8x + 12 = 180
    19x + 28 = 180
    19x = 180 - 28
    19x = 152
       x = 152/19
       x = 8 <==

18. 3x + 17 = 5x - 47...vertical angles are equal
      3x - 5x = -47 - 17
      -2x = - 64
         x = -64/-2
         x = 32 <==

       2y + 9 = 3y - 20
       2y - 3y = -20 - 9
       -y = -29
        y = 29 <==