| 12 | − | 4 | ( | X | + | 3 | ) | = | - | 7 | ( | X | + | 3 | ) |
| Left side of the equation = | 12 | − | 4 | X | − | 4 | × | 3 |
| = | 12 | − | 4 | X | − | 12 |
| = | 0 | − | 4 | X |
| 0 | − | 4 | X | = | - | 7 | ( | X | + | 3 | ) |
| Right side of the equation = | - | 7 | X | − | 7 | × | 3 |
| = | - | 7 | X | − | 21 |
| - | 4 | X | = | - | 7 | X | − | 21 |
| - | 4 | X | + | 7 | X | = | - | 21 |
| 3 | X | = | - | 21 |
| X | = | - | 21 | ÷ | 3 |
| = | - | 21 | × | 1 3 |
| = | - | 7 | × | 1 |
| X | = | - | 7 |