| 390 | ( | 340 | + | v | ) | = | 440 | ( | 340 | + | v | ) |
| 方程左边 = | 390 | × | 340 | + | 390 | v |
| = | 132600 | + | 390 | v |
| 132600 | + | 390 | v | = | 440 | ( | 340 | + | v | ) |
| 方程右边 = | 440 | × | 340 | + | 440 | v |
| = | 149600 | + | 440 | v |
| 132600 | + | 390 | v | = | 149600 | + | 440 | v |
| 390 | v | − | 440 | v | = | 149600 | − | 132600 |
| - | 50 | v | = | 149600 | − | 132600 |
| - | 50 | v | = | 17000 |
| - | 17000 | = | 50 | v |
| 50 | v | = | - | 17000 |
| v | = | - | 17000 | ÷ | 50 |
| = | - | 17000 | × | 1 50 |
| = | - | 340 | × | 1 |
| v | = | - | 340 |