| 6 | x | + | 42 | − | 3 | = | 12 | − | 4 | x | + | 3 |
| Left side of the equation = | 6 | x | + | 39 |
| 6 | x | + | 39 | = | 12 | − | 4 | x | + | 3 |
| Right side of the equation = | 15 | − | 4 | x |
| 6 | x | + | 39 | = | 15 | − | 4 | x |
| 6 | x | + | 4 | x | = | 15 | − | 39 |
| 10 | x | = | 15 | − | 39 |
| 10 | x | = | - | 24 |
| x | = | - | 24 | ÷ | 10 |
| = | - | 24 | × | 1 10 |
| = | - | 12 | × | 1 5 |
| x | = | - | 12 5 |
| x | = | - 2.4 |