Question 803547
1st angle = 5x
2nd angle = 8x - 1
3rd angle = 12x + 6
angles 1 + 2 + 3 = 180
5x + (8x - 1) + (12x + 6) = 180
5x + 8x + 12x - 1 + 6 = 180
25x + 5 = 180
25x + 5 - 5 = 180 - 5
25x = 175
25x/25 = 175/25
x = 7

1st angle = 5(7) 
          = 35 degrees
2nd angle = 8(7) - 1
          = 56 - 1
          = 55 degrees
3rd angle = 12(7) + 6
          = 84 + 6
          = 90
35 + 55 + 90 = 180
180 = 180