| ( | x | + | 20 | ) | × | 12 | = | ( | x | − | 20 | ) | × | 16 |
| 方程左边 = | x | × | 12 | + | 20 | × | 12 |
| = | x | × | 12 | + | 240 |
| 12 | x | + | 240 | = | ( | x | − | 20 | ) | × | 16 |
| 方程右边 = | x | × | 16 | − | 20 | × | 16 |
| = | x | × | 16 | − | 320 |
| 12 | x | + | 240 | = | 16 | x | − | 320 |
| 12 | x | − | 16 | x | = | - | 320 | − | 240 |
| - | 4 | x | = | - | 320 | − | 240 |
| - | 4 | x | = | - | 560 |
| 560 | = | 4 | x |
| 4 | x | = | 560 |
| x | = | 560 | ÷ | 4 |
| = | 560 | × | 1 4 |
| = | 140 | × | 1 |
| x | = | 140 |