| 2 | ( | 12 | + | 7 20 | x | ) | = | 3 | ( | x | − | ( | 12 | + | 7 20 | x | ) | ) |
| 方程左边 = | 2 | × | 12 | + | 2 | × | 7 20 | x |
| = | 24 | + | 7 10 | x |
| 24 | + | 7 10 | x | = | 3 | ( | x | − | ( | 12 | + | 7 20 | x | ) | ) |
| 方程右边 = | 3 | x | − | 3 | ( | 12 | + | 7 20 | x | ) |
| = | 3 | x | − | 3 | × | 12 | − | 3 | × | 7 20 | x |
| = | 3 | x | − | 36 | − | 21 20 | x |
| = | 39 20 | x | − | 36 |
| 24 | + | 7 10 | x | = | 39 20 | x | − | 36 |
7 10 | x | − | 39 20 | x | = | - | 36 | − | 24 |
| - | 5 4 | x | = | - | 36 | − | 24 |
| - | 5 4 | x | = | - | 60 |
| 60 | = | 5 4 | x |
5 4 | x | = | 60 |
| x | = | 60 | ÷ | 5 4 |
| = | 60 | × | 4 5 |
| = | 12 | × | 4 |
| x | = | 48 |