| X | × | 30 | × | 4 5 | = | ( | X | − | 5 | ) | × | 9 10 | × | 30 |
| 方程左边 = | X | × | 24 |
| 24 | X | = | ( | X | − | 5 | ) | × | 9 10 | × | 30 |
| 方程右边 = | ( | X | − | 5 | ) | × | 27 |
| 24 | X | = | ( | X | − | 5 | ) | × | 27 |
| 方程右边 = | X | × | 27 | − | 5 | × | 27 |
| = | X | × | 27 | − | 135 |
| 24 | X | = | 27 | X | − | 135 |
| 24 | X | − | 27 | X | = | - | 135 |
| - | 3 | X | = | - | 135 |
| 135 | = | 3 | X |
| 3 | X | = | 135 |
| X | = | 135 | ÷ | 3 |
| = | 135 | × | 1 3 |
| = | 45 | × | 1 |
| X | = | 45 |