| 3 | × | 10 | x | − | 2 | ( | 31 | x | − | 13 | ) | = | 6 |
| 方程左边 = | 30 | x | − | 2 | ( | 31 | x | − | 13 | ) |
| 30 | x | − | 2 | ( | 31 | x | − | 13 | ) | = | 6 |
| 方程左边 = | 30 | x | − | 2 | × | 31 | x | + | 2 | × | 13 |
| = | 30 | x | − | 62 | x | + | 26 |
| = | - | 32 | x | + | 26 |
| - | 32 | x | + | 26 | = | 6 |
| - | 32 | x | = | 6 | − | 26 |
| - | 32 | x | = | - | 20 |
| 20 | = | 32 | x |
| 32 | x | = | 20 |
| x | = | 20 | ÷ | 32 |
| = | 20 | × | 1 32 |
| = | 5 | × | 1 8 |
| x | = | 5 8 |
| x | = | 0.625 |