Simplifying 3x + -8 = 31 Reorder the terms: -8 + 3x = 31 Solving -8 + 3x = 31 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '8' to each side of the equation. -8 + 8 + 3x = 31 + 8 Combine like terms: -8 + 8 = 0 0 + 3x = 31 + 8 3x = 31 + 8 Combine like terms: 31 + 8 = 39 3x = 39 Divide each side by '3'. x = 13 Simplifying x = 13