| 15 | ( | t | − | 56 | ) | = | 13 | ( | 80 | − | t | ) |
| 方程左边 = | 15 | t | − | 15 | × | 56 |
| = | 15 | t | − | 840 |
| 15 | t | − | 840 | = | 13 | ( | 80 | − | t | ) |
| 方程右边 = | 13 | × | 80 | − | 13 | t |
| = | 1040 | − | 13 | t |
| 15 | t | − | 840 | = | 1040 | − | 13 | t |
| 15 | t | + | 13 | t | = | 1040 | + | 840 |
| 28 | t | = | 1040 | + | 840 |
| 28 | t | = | 1880 |
| t | = | 1880 | ÷ | 28 |
| = | 1880 | × | 1 28 |
| = | 470 | × | 1 7 |
| t | = | 470 7 |
| t | = | 67.142857 |