| ( | 68 | − | 51 | ) | ÷ | ( | 51 | − | 40 | ) | = | ( | 85 | − | t | ) | ÷ | ( | t | − | 71 | ) |
| 方程两边同时乘以: | ( | 51 | − | 40 | ) | , | ( | t | − | 71 | ) |
| ( | 68 | − | 51 | ) | ( | t | − | 71 | ) | = | ( | 85 | − | t | ) | ( | 51 | − | 40 | ) |
| 68 | ( | t | − | 71 | ) | − | 51 | ( | t | − | 71 | ) | = | ( | 85 | − | t | ) | ( | 51 | − | 40 | ) |
| 68 | ( | t | − | 71 | ) | − | 51 | ( | t | − | 71 | ) | = | 85 | ( | 51 | − | 40 | ) | − | t | ( | 51 | − | 40 | ) |
| 68 | t | − | 68 | × | 71 | − | 51 | ( | t | − | 71 | ) | = | 85 | ( | 51 | − | 40 | ) | − | t | ( | 51 | − | 40 | ) |
| 68 | t | − | 68 | × | 71 | − | 51 | ( | t | − | 71 | ) | = | 85 | × | 51 | − | 85 | × | 40 | − | t | ( | 51 | − | 40 | ) |
| 68 | t | − | 4828 | − | 51 | ( | t | − | 71 | ) | = | 4335 | − | 3400 | − | t | ( | 51 | − | 40 | ) |
| 68 | t | − | 4828 | − | 51 | ( | t | − | 71 | ) | = | 935 | − | t | ( | 51 | − | 40 | ) |
| 68 | t | − | 4828 | − | 51 | t | + | 51 | × | 71 | = | 935 | − | t | ( | 51 | − | 40 | ) |
| 68 | t | − | 4828 | − | 51 | t | + | 51 | × | 71 | = | 935 | − | t | × | 51 | + | t | × | 40 |
| 68 | t | − | 4828 | − | 51 | t | + | 3621 | = | 935 | − | t | × | 51 | + | t | × | 40 |
| 17 | t | − | 1207 | = | 935 | − | 11 | t |
| 17 | t | + | 11 | t | = | 935 | + | 1207 |
| 28 | t | = | 935 | + | 1207 |
| 28 | t | = | 2142 |
| t | = | 2142 | ÷ | 28 |
| = | 2142 | × | 1 28 |
| = | 153 | × | 1 2 |
| t | = | 153 2 |
| t | = | 76.5 |