| 42 | ( | t | − | 25 | ) | = | 3 | ( | 1200 | − | t | ) |
| 方程左边 = | 42 | t | − | 42 | × | 25 |
| = | 42 | t | − | 1050 |
| 42 | t | − | 1050 | = | 3 | ( | 1200 | − | t | ) |
| 方程右边 = | 3 | × | 1200 | − | 3 | t |
| = | 3600 | − | 3 | t |
| 42 | t | − | 1050 | = | 3600 | − | 3 | t |
| 42 | t | + | 3 | t | = | 3600 | + | 1050 |
| 45 | t | = | 3600 | + | 1050 |
| 45 | t | = | 4650 |
| t | = | 4650 | ÷ | 45 |
| = | 4650 | × | 1 45 |
| = | 310 | × | 1 3 |
| t | = | 310 3 |
| t | = | 103.333333 |