| ( | x | − | 20 | ( | 600 | − | 10 | x | ) | ) | = | 3840 |
| 方程左边 = | x | − | 20 | ( | 600 | − | 10 | x | ) |
| = | x | − | 20 | × | 600 | + | 20 | × | 10 | x |
| = | x | − | 12000 | + | 200 | x |
| = | 201 | x | − | 12000 |
| 201 | x | − | 12000 | = | 3840 |
| 201 | x | = | 3840 | + | 12000 |
| 201 | x | = | 15840 |
| x | = | 15840 | ÷ | 201 |
| = | 15840 | × | 1 201 |
| = | 5280 | × | 1 67 |
| x | = | 5280 67 |
| x | = | 78.80597 |