| ( | 2500 | + | 300 | + | 200 | ) | + | ( | x | − | 30000 | ) | × | 3 100 | = | x | × | 1 20 |
| 方程左边 = | 2500 | + | 300 | + | 200 | + | ( | x | − | 30000 | ) | × | 3 100 |
| = | 3000 | + | ( | x | − | 30000 | ) | × | 3 100 |
| = | 3000 | + | x | × | 3 100 | − | 30000 | × | 3 100 |
| = | 3000 | + | x | × | 3 100 | − | 900 |
| = | 2100 | + | 3 100 | x |
| 2100 | + | 3 100 | x | = | x | × | 1 20 |
3 100 | x | − | 1 20 | x | = | - | 2100 |
| - | 1 50 | x | = | - | 2100 |
| 2100 | = | 1 50 | x |
1 50 | x | = | 2100 |
| x | = | 2100 | ÷ | 1 50 |
| = | 2100 | × | 50 |
| x | = | 105000 |