| 30 | × | 200 | + | ( | x | − | 30 | ) | × | 100 | = | 0 |
| 方程左边 = | 6000 | + | ( | x | − | 30 | ) | × | 100 |
| 6000 | + | ( | x | − | 30 | ) | × | 100 | = | 0 |
| 方程左边 = | 6000 | + | x | × | 100 | − | 30 | × | 100 |
| = | 6000 | + | x | × | 100 | − | 3000 |
| = | 3000 | + | 100 | x |
| 3000 | + | 100 | x | = | 0 |
| 100 | x | = | 0 | − | 3000 |
| 100 | x | = | - | 3000 |
| x | = | - | 3000 | ÷ | 100 |
| = | - | 3000 | × | 1 100 |
| = | - | 30 | × | 1 |
| x | = | - | 30 |