| 30 | ( | x | − | 200 | ) | = | ( | 20 | + | 30 | ) | x |
| 方程左边 = | 30 | x | − | 30 | × | 200 |
| = | 30 | x | − | 6000 |
| 30 | x | − | 6000 | = | ( | 20 | + | 30 | ) | x |
| 方程右边 = | 20 | x | + | 30 | x |
| = | 50 | x |
| 30 | x | − | 6000 | = | 50 | x |
| 30 | x | − | 50 | x | = | 6000 |
| - | 20 | x | = | 6000 |
| - | 6000 | = | 20 | x |
| 20 | x | = | - | 6000 |
| x | = | - | 6000 | ÷ | 20 |
| = | - | 6000 | × | 1 20 |
| = | - | 300 | × | 1 |
| x | = | - | 300 |