| ( | 2000 | − | 6800 | + | X | ) | × | 10 100 | ÷ | 4 | = | 880 |
| 方程左边 = | ( | 2000 | − | 6800 | + | X | ) | × | 1 40 |
| ( | 2000 | − | 6800 | + | X | ) | × | 1 40 | = | 880 |
| 方程左边 = | 2000 | × | 1 40 | − | 6800 | × | 1 40 | + | X | × | 1 40 |
| = | 50 | − | 170 | + | X | × | 1 40 |
| = | - | 120 | + | 1 40 | X |
| - | 120 | + | 1 40 | X | = | 880 |
1 40 | X | = | 880 | + | 120 |
1 40 | X | = | 1000 |
| X | = | 1000 | ÷ | 1 40 |
| = | 1000 | × | 40 |
| X | = | 40000 |