| 210 | + | ( | x | − | 210 | ) | × | 20 100 | = | ( | 2 | ÷ | 5 | ) | x |
| 方程左边 = | 210 | + | x | × | 20 100 | − | 210 | × | 20 100 |
| = | 210 | + | x | × | 20 100 | − | 42 |
| = | 168 | + | 20 100 | x |
| 168 | + | 20 100 | x | = | ( | 2 | ÷ | 5 | ) | x |
| 方程右边 = | 2 | ÷ | 5 | × | x |
| = | 2 5 | x |
| 168 | + | 20 100 | x | = | 2 5 | x |
20 100 | x | − | 2 5 | x | = | - | 168 |
| - | 1 5 | x | = | - | 168 |
| 168 | = | 1 5 | x |
1 5 | x | = | 168 |
| x | = | 168 | ÷ | 1 5 |
| = | 168 | × | 5 |
| x | = | 840 |