6r + 7 = 13 + 7r
6r + 7 - 7r = 13
6r - 7r = 13 - 7
-r = 6
r = -6
13 - 14x = 1 - x
13 = 1 - x + 14x
13 - 1 = -x + 14x
12 = 13x
x = 12/13
2(x+7) + x = -20
2x + 14 + x = -20
2x + x = -20 - 14
3x = -34
x = -34/3
-8 - x = x - 4x
-8 = x - 4x + x
-8 = -2x
x = 4
