| 3000 | + | 4000 | x | = | 21000 | ( | 2400 | x | − | 20000 | ÷ | 200 | ) |
| 方程右边 = | 21000 | × | 2400 | x | − | 21000 | × | 20000 | ÷ | 200 |
| = | 50400000 | x | − | 2100000 |
| 3000 | + | 4000 | x | = | 50400000 | x | − | 2100000 |
| 4000 | x | − | 50400000 | x | = | - | 2100000 | − | 3000 |
| - | 50396000 | x | = | - | 2100000 | − | 3000 |
| - | 50396000 | x | = | - | 2103000 |
| 2103000 | = | 50396000 | x |
| 50396000 | x | = | 2103000 |
| x | = | 2103000 | ÷ | 50396000 |
| = | 2103000 | × | 1 50396000 |
| = | 2103 | × | 1 50396 |
| x | = | 2103 50396 |
| x | = | 0.04173 |