| ( | 68 | − | 53 | ) | ÷ | ( | 53 | − | 40 | ) | = | ( | 85 | − | t | ) | ÷ | ( | t | − | 71 | ) |
| 方程两边同时乘以: | ( | 53 | − | 40 | ) | , | ( | t | − | 71 | ) |
| ( | 68 | − | 53 | ) | ( | t | − | 71 | ) | = | ( | 85 | − | t | ) | ( | 53 | − | 40 | ) |
| 68 | ( | t | − | 71 | ) | − | 53 | ( | t | − | 71 | ) | = | ( | 85 | − | t | ) | ( | 53 | − | 40 | ) |
| 68 | ( | t | − | 71 | ) | − | 53 | ( | t | − | 71 | ) | = | 85 | ( | 53 | − | 40 | ) | − | t | ( | 53 | − | 40 | ) |
| 68 | t | − | 68 | × | 71 | − | 53 | ( | t | − | 71 | ) | = | 85 | ( | 53 | − | 40 | ) | − | t | ( | 53 | − | 40 | ) |
| 68 | t | − | 68 | × | 71 | − | 53 | ( | t | − | 71 | ) | = | 85 | × | 53 | − | 85 | × | 40 | − | t | ( | 53 | − | 40 | ) |
| 68 | t | − | 4828 | − | 53 | ( | t | − | 71 | ) | = | 4505 | − | 3400 | − | t | ( | 53 | − | 40 | ) |
| 68 | t | − | 4828 | − | 53 | ( | t | − | 71 | ) | = | 1105 | − | t | ( | 53 | − | 40 | ) |
| 68 | t | − | 4828 | − | 53 | t | + | 53 | × | 71 | = | 1105 | − | t | ( | 53 | − | 40 | ) |
| 68 | t | − | 4828 | − | 53 | t | + | 53 | × | 71 | = | 1105 | − | t | × | 53 | + | t | × | 40 |
| 68 | t | − | 4828 | − | 53 | t | + | 3763 | = | 1105 | − | t | × | 53 | + | t | × | 40 |
| 15 | t | − | 1065 | = | 1105 | − | 13 | t |
| 15 | t | + | 13 | t | = | 1105 | + | 1065 |
| 28 | t | = | 1105 | + | 1065 |
| 28 | t | = | 2170 |
| t | = | 2170 | ÷ | 28 |
| = | 2170 | × | 1 28 |
| = | 155 | × | 1 2 |
| t | = | 155 2 |
| t | = | 77.5 |