| ( | 330 | − | X | ) | ÷ | 330 | × | 100 | = | 7 |
| 方程左边 = | ( | 330 | − | X | ) | × | 10 33 |
| ( | 330 | − | X | ) | × | 10 33 | = | 7 |
| 方程左边 = | 330 | × | 10 33 | − | X | × | 10 33 |
| = | 100 | − | X | × | 10 33 |
| 100 | − | 10 33 | X | = | 7 |
| - | 10 33 | X | = | 7 | − | 100 |
| - | 10 33 | X | = | - | 93 |
| 93 | = | 10 33 | X |
10 33 | X | = | 93 |
| X | = | 93 | ÷ | 10 33 |
| = | 93 | × | 33 10 |
| X | = | 3069 10 |
| X | = | 306.9 |