| 5 | − | ( | 10 | x | − | 21 | ) | ÷ | 5 | = | 3 | x | ÷ | 10 |
| 方程左边 = | 5 | − | 10 | x | × | 1 5 | + | 21 | × | 1 5 |
| = | 5 | − | 2 | x | + | 21 5 |
| = | 46 5 | − | 2 | x |
46 5 | − | 2 | x | = | 3 | x | ÷ | 10 |
| 方程右边 = | 3 10 | x |
46 5 | − | 2 | x | = | 3 10 | x |
| - | 2 | x | − | 3 10 | x | = | - | 46 5 |
| - | 23 10 | x | = | - | 46 5 |
46 5 | = | 23 10 | x |
23 10 | x | = | 46 5 |
| x | = | 46 5 | ÷ | 23 10 |
| = | 46 5 | × | 10 23 |
| = | 2 | × | 2 |
| x | = | 4 |