| X | − | ( | ( | X | − | X | × | 1 5 | ) | × | 1 5 | ) | − | ( | X | ÷ | ( | 1 | + | 3 100 | ) | ) | = | 4000 |
| X | − | ( | X | − | X | × | 1 5 | ) | × | 1 5 | − | ( | X | ÷ | ( | 1 | + | 3 100 | ) | ) | = | 4000 |
| X | − | X | × | 1 5 | + | X | × | 1 5 | × | 1 5 | − | ( | X | ÷ | ( | 1 | + | 3 100 | ) | ) | = | 4000 |
| X | − | X | × | 1 5 | + | X | × | 1 25 | − | ( | X | ÷ | ( | 1 | + | 3 100 | ) | ) | = | 4000 |
21 25 | X | − | ( | X | ÷ | ( | 1 | + | 3 100 | ) | ) | = | 4000 |
21 25 | X | − | X | ÷ | ( | 1 | + | 3 100 | ) | = | 4000 |
| 方程两边同时乘以: | ( | 1 | + | 3 100 | ) |
21 25 | X | ( | 1 | + | 3 100 | ) | − | X | = | 4000 | ( | 1 | + | 3 100 | ) |
21 25 | X | × | 1 | + | 21 25 | X | × | 3 100 | − | X | = | 4000 | ( | 1 | + | 3 100 | ) |
21 25 | X | × | 1 | + | 21 25 | X | × | 3 100 | − | X | = | 4000 | × | 1 | + | 4000 | × | 3 100 |
21 25 | X | + | 63 2500 | X | − | X | = | 4000 | + | 120 |
| - | 337 2500 | X | = | 4120 |
| - | 4120 | = | 337 2500 | X |
337 2500 | X | = | - | 4120 |
| X | = | - | 4120 | ÷ | 337 2500 |
| = | - | 4120 | × | 2500 337 |
| X | = | - | 10300000 337 |
| X | = | - 30563.79822 |