Greetings from Brasil...
Let's add all the values on one side and make it equal to the sum of all the other values on the other side
(- X) + (- X) + (- X) + (- X) + (- X) + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = X + X + X + (- 1) + (- 1) + (- 1) + (- 1) + (- 1) + (- 1) + (- 1) + (- 1)
- 5X + 12 = 3X - 8
- 5X - 3X = - 8 - 12
- 8X = - 20 x(- 1)
8X = 20
X = 20/8
X = 5/2
or X = 2.5