| ( | 19 | − | 18 | ) | ÷ | ( | 18 | − | 8 | ) | = | ( | 40 | − | t | ) | ÷ | ( | t | − | 30 | ) |
| 方程两边同时乘以: | ( | 18 | − | 8 | ) | , | ( | t | − | 30 | ) |
| ( | 19 | − | 18 | ) | ( | t | − | 30 | ) | = | ( | 40 | − | t | ) | ( | 18 | − | 8 | ) |
| 19 | ( | t | − | 30 | ) | − | 18 | ( | t | − | 30 | ) | = | ( | 40 | − | t | ) | ( | 18 | − | 8 | ) |
| 19 | ( | t | − | 30 | ) | − | 18 | ( | t | − | 30 | ) | = | 40 | ( | 18 | − | 8 | ) | − | t | ( | 18 | − | 8 | ) |
| 19 | t | − | 19 | × | 30 | − | 18 | ( | t | − | 30 | ) | = | 40 | ( | 18 | − | 8 | ) | − | t | ( | 18 | − | 8 | ) |
| 19 | t | − | 19 | × | 30 | − | 18 | ( | t | − | 30 | ) | = | 40 | × | 18 | − | 40 | × | 8 | − | t | ( | 18 | − | 8 | ) |
| 19 | t | − | 570 | − | 18 | ( | t | − | 30 | ) | = | 720 | − | 320 | − | t | ( | 18 | − | 8 | ) |
| 19 | t | − | 570 | − | 18 | ( | t | − | 30 | ) | = | 400 | − | t | ( | 18 | − | 8 | ) |
| 19 | t | − | 570 | − | 18 | t | + | 18 | × | 30 | = | 400 | − | t | ( | 18 | − | 8 | ) |
| 19 | t | − | 570 | − | 18 | t | + | 18 | × | 30 | = | 400 | − | t | × | 18 | + | t | × | 8 |
| 19 | t | − | 570 | − | 18 | t | + | 540 | = | 400 | − | t | × | 18 | + | t | × | 8 |
| 1 | t | − | 30 | = | 400 | − | 10 | t |
| 1 | t | + | 10 | t | = | 400 | + | 30 |
| 11 | t | = | 400 | + | 30 |
| 11 | t | = | 430 |
| t | = | 430 | ÷ | 11 |
| = | 430 | × | 1 11 |
| t | = | 430 11 |
| t | = | 39.090909 |