| ( | ( | 30 | − | x | ) | × | 15000 | ) | ÷ | 1200000 | = | 40 100 |
| 方程左边 = | ( | 30 | − | x | ) | × | 15000 | × | 1 1200000 |
| = | ( | 30 | − | x | ) | × | 1 80 |
| = | 30 | × | 1 80 | − | x | × | 1 80 |
| = | 3 8 | − | x | × | 1 80 |
3 8 | − | 1 80 | x | = | 40 100 |
| - | 1 80 | x | = | 40 100 | − | 3 8 |
| - | 1 80 | x | = | 1 40 |
| - | 1 40 | = | 1 80 | x |
1 80 | x | = | - | 1 40 |
| x | = | - | 1 40 | ÷ | 1 80 |
| = | - | 1 40 | × | 80 |
| = | - | 1 | × | 2 |
| x | = | - | 2 |