| ( | 12 | x | − | 12 | ) | × | 12 | − | 5 | x | × | 12 | = | 108 |
| 方程左边 = | ( | 12 | x | − | 12 | ) | × | 12 | − | 60 | x |
| ( | 12 | x | − | 12 | ) | × | 12 | − | 60 | x | = | 108 |
| 方程左边 = | 12 | x | × | 12 | − | 12 | × | 12 | − | 60 | x |
| = | 144 | x | − | 144 | − | 60 | x |
| = | 84 | x | − | 144 |
| 84 | x | − | 144 | = | 108 |
| 84 | x | = | 108 | + | 144 |
| 84 | x | = | 252 |
| x | = | 252 | ÷ | 84 |
| = | 252 | × | 1 84 |
| = | 3 | × | 1 |
| x | = | 3 |