| 15 | ( | 80 | − | t | ) | = | 9 | ( | t | − | 56 | ) |
| 方程左边 = | 15 | × | 80 | − | 15 | t |
| = | 1200 | − | 15 | t |
| 1200 | − | 15 | t | = | 9 | ( | t | − | 56 | ) |
| 方程右边 = | 9 | t | − | 9 | × | 56 |
| = | 9 | t | − | 504 |
| 1200 | − | 15 | t | = | 9 | t | − | 504 |
| - | 15 | t | − | 9 | t | = | - | 504 | − | 1200 |
| - | 24 | t | = | - | 504 | − | 1200 |
| - | 24 | t | = | - | 1704 |
| 1704 | = | 24 | t |
| 24 | t | = | 1704 |
| t | = | 1704 | ÷ | 24 |
| = | 1704 | × | 1 24 |
| = | 71 | × | 1 |
| t | = | 71 |