| ( | 40 | − | x | ) | × | 15 | = | ( | 60 | − | x | ) | × | 9 |
| 方程左边 = | 40 | × | 15 | − | x | × | 15 |
| = | 600 | − | x | × | 15 |
| 600 | − | 15 | x | = | ( | 60 | − | x | ) | × | 9 |
| 方程右边 = | 60 | × | 9 | − | x | × | 9 |
| = | 540 | − | x | × | 9 |
| 600 | − | 15 | x | = | 540 | − | 9 | x |
| - | 15 | x | + | 9 | x | = | 540 | − | 600 |
| - | 6 | x | = | 540 | − | 600 |
| - | 6 | x | = | - | 60 |
| 60 | = | 6 | x |
| 6 | x | = | 60 |
| x | = | 60 | ÷ | 6 |
| = | 60 | × | 1 6 |
| = | 10 | × | 1 |
| x | = | 10 |