| 15 | + | ( | 40 | − | x | ) | = | 3 2 | ( | 20 | + | x | ) |
| 方程左边 = | 15 | + | 40 | − | x |
| = | 55 | − | x |
| 55 | − | x | = | 3 2 | ( | 20 | + | x | ) |
| 方程右边 = | 3 2 | × | 20 | + | 3 2 | x |
| = | 30 | + | 3 2 | x |
| 55 | − | x | = | 30 | + | 3 2 | x |
| - | x | − | 3 2 | x | = | 30 | − | 55 |
| - | 5 2 | x | = | 30 | − | 55 |
| - | 5 2 | x | = | - | 25 |
| 25 | = | 5 2 | x |
5 2 | x | = | 25 |
| x | = | 25 | ÷ | 5 2 |
| = | 25 | × | 2 5 |
| = | 5 | × | 2 |
| x | = | 10 |