| 3 | ( | x | + | 6 | ) | + | 3 | x | = | 3 | ( | - | 9 | − | x | ) |
| 方程左边 = | 3 | x | + | 3 | × | 6 | + | 3 | x |
| = | 3 | x | + | 18 | + | 3 | x |
| = | 6 | x | + | 18 |
| 6 | x | + | 18 | = | 3 | ( | - | 9 | − | x | ) |
| 方程右边 = | - | 3 | × | 9 | − | 3 | x |
| = | - | 27 | − | 3 | x |
| 6 | x | + | 18 | = | - | 27 | − | 3 | x |
| 6 | x | + | 3 | x | = | - | 27 | − | 18 |
| 9 | x | = | - | 27 | − | 18 |
| 9 | x | = | - | 45 |
| x | = | - | 45 | ÷ | 9 |
| = | - | 45 | × | 1 9 |
| = | - | 5 | × | 1 |
| x | = | - | 5 |