| ( | 30 | + | 80 | − | X | ) | = | 3 2 | ( | 40 | + | X | ) |
| 方程左边 = | 30 | + | 80 | − | X |
| = | 110 | − | X |
| 110 | − | X | = | 3 2 | ( | 40 | + | X | ) |
| 方程右边 = | 3 2 | × | 40 | + | 3 2 | X |
| = | 60 | + | 3 2 | X |
| 110 | − | X | = | 60 | + | 3 2 | X |
| - | X | − | 3 2 | X | = | 60 | − | 110 |
| - | 5 2 | X | = | 60 | − | 110 |
| - | 5 2 | X | = | - | 50 |
| 50 | = | 5 2 | X |
5 2 | X | = | 50 |
| X | = | 50 | ÷ | 5 2 |
| = | 50 | × | 2 5 |
| = | 10 | × | 2 |
| X | = | 20 |