| 7 | ( | X | − | 5 | ) | = | 1 5 | ( | X | + | 63 | ) |
| 方程左边 = | 7 | X | − | 7 | × | 5 |
| = | 7 | X | − | 35 |
| 7 | X | − | 35 | = | 1 5 | ( | X | + | 63 | ) |
| 方程右边 = | 1 5 | X | + | 1 5 | × | 63 |
| = | 1 5 | X | + | 63 5 |
| 7 | X | − | 35 | = | 1 5 | X | + | 63 5 |
| 7 | X | − | 1 5 | X | = | 63 5 | + | 35 |
34 5 | X | = | 63 5 | + | 35 |
34 5 | X | = | 238 5 |
| X | = | 238 5 | ÷ | 34 5 |
| = | 238 5 | × | 5 34 |
| = | 7 | × | 1 |
| X | = | 7 |