| 640 | ( | x | − | 40 | ) | = | 700 | ( | x | − | 88 | ) |
| 方程左边 = | 640 | x | − | 640 | × | 40 |
| = | 640 | x | − | 25600 |
| 640 | x | − | 25600 | = | 700 | ( | x | − | 88 | ) |
| 方程右边 = | 700 | x | − | 700 | × | 88 |
| = | 700 | x | − | 61600 |
| 640 | x | − | 25600 | = | 700 | x | − | 61600 |
| 640 | x | − | 700 | x | = | - | 61600 | + | 25600 |
| - | 60 | x | = | - | 61600 | + | 25600 |
| - | 60 | x | = | - | 36000 |
| 36000 | = | 60 | x |
| 60 | x | = | 36000 |
| x | = | 36000 | ÷ | 60 |
| = | 36000 | × | 1 60 |
| = | 600 | × | 1 |
| x | = | 600 |