| ( | x | + | 6 | ) | × | 20 | = | ( | x | + | 6 | + | x | ) | × | 12 |
| 方程左边 = | x | × | 20 | + | 6 | × | 20 |
| = | x | × | 20 | + | 120 |
| 20 | x | + | 120 | = | ( | x | + | 6 | + | x | ) | × | 12 |
| 方程右边 = | x | × | 12 | + | 6 | × | 12 | + | x | × | 12 |
| = | x | × | 12 | + | 72 | + | x | × | 12 |
| = | 24 | x | + | 72 |
| 20 | x | + | 120 | = | 24 | x | + | 72 |
| 20 | x | − | 24 | x | = | 72 | − | 120 |
| - | 4 | x | = | 72 | − | 120 |
| - | 4 | x | = | - | 48 |
| 48 | = | 4 | x |
| 4 | x | = | 48 |
| x | = | 48 | ÷ | 4 |
| = | 48 | × | 1 4 |
| = | 12 | × | 1 |
| x | = | 12 |