| 4200 | ( | 70 | − | t | ) | = | 12600 | ( | t | − | 50 | ) |
| 方程左边 = | 4200 | × | 70 | − | 4200 | t |
| = | 294000 | − | 4200 | t |
| 294000 | − | 4200 | t | = | 12600 | ( | t | − | 50 | ) |
| 方程右边 = | 12600 | t | − | 12600 | × | 50 |
| = | 12600 | t | − | 630000 |
| 294000 | − | 4200 | t | = | 12600 | t | − | 630000 |
| - | 4200 | t | − | 12600 | t | = | - | 630000 | − | 294000 |
| - | 16800 | t | = | - | 630000 | − | 294000 |
| - | 16800 | t | = | - | 924000 |
| 924000 | = | 16800 | t |
| 16800 | t | = | 924000 |
| t | = | 924000 | ÷ | 16800 |
| = | 924000 | × | 1 16800 |
| = | 55 | × | 1 |
| t | = | 55 |