| ( | 60 | − | x | ) | ÷ | ( | x | − | 40 | ) | = | 3 |
| 方程两边同时乘以: | ( | x | − | 40 | ) |
| ( | 60 | − | x | ) | = | 3 | ( | x | − | 40 | ) |
| 60 | − | x | = | 3 | ( | x | − | 40 | ) |
| 60 | − | x | = | 3 | x | − | 3 | × | 40 |
| 60 | − | x | = | 3 | x | − | 120 |
| - | x | − | 3 | x | = | - | 120 | − | 60 |
| - | 4 | x | = | - | 120 | − | 60 |
| - | 4 | x | = | - | 180 |
| 180 | = | 4 | x |
| 4 | x | = | 180 |
| x | = | 180 | ÷ | 4 |
| = | 180 | × | 1 4 |
| = | 45 | × | 1 |
| x | = | 45 |