| 20 | x | × | 80 100 | = | ( | x | − | 7 | ) | × | 20 | × | 90 100 |
| 方程左边 = | 16 | x |
| 16 | x | = | ( | x | − | 7 | ) | × | 20 | × | 90 100 |
| 方程右边 = | ( | x | − | 7 | ) | × | 18 |
| 16 | x | = | ( | x | − | 7 | ) | × | 18 |
| 方程右边 = | x | × | 18 | − | 7 | × | 18 |
| = | x | × | 18 | − | 126 |
| 16 | x | = | 18 | x | − | 126 |
| 16 | x | − | 18 | x | = | - | 126 |
| - | 2 | x | = | - | 126 |
| 126 | = | 2 | x |
| 2 | x | = | 126 |
| x | = | 126 | ÷ | 2 |
| = | 126 | × | 1 2 |
| = | 63 | × | 1 |
| x | = | 63 |