| ( | 12 | − | 3 | ) | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) | = | 128 | − | ( | 30 | − | ( | 7 | + | ( | 5 | − | 2 | ) | ) | ) |
| 方程左边 = | 12 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 12 | × | 2 | ( | 3 | − | 2 | ) | + | 12 | X | ( | 3 | − | 2 | ) | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 24 | ( | 3 | − | 2 | ) | + | 12 | X | ( | 3 | − | 2 | ) | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 24 | × | 3 | − | 24 | × | 2 | + | 12 | X | ( | 3 | − | 2 | ) | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 72 | − | 48 | + | 12 | X | ( | 3 | − | 2 | ) | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 24 | + | 12 | X | ( | 3 | − | 2 | ) | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 24 | + | 12 | X | × | 3 | − | 12 | X | × | 2 | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 24 | + | 36 | X | − | 24 | X | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 24 | + | 12 | X | − | 3 | ( | 2 | + | X | ) | ( | 3 | − | 2 | ) |
| = | 24 | + | 12 | X | − | 3 | × | 2 | ( | 3 | − | 2 | ) | − | 3 | X | ( | 3 | − | 2 | ) |
| = | 24 | + | 12 | X | − | 6 | ( | 3 | − | 2 | ) | − | 3 | X | ( | 3 | − | 2 | ) |
| = | 24 | + | 12 | X | − | 6 | × | 3 | + | 6 | × | 2 | − | 3 | X | ( | 3 | − | 2 | ) |
| = | 24 | + | 12 | X | − | 18 | + | 12 | − | 3 | X | ( | 3 | − | 2 | ) |
| = | 18 | + | 12 | X | − | 3 | X | ( | 3 | − | 2 | ) |
| = | 18 | + | 12 | X | − | 3 | X | × | 3 | + | 3 | X | × | 2 |
| = | 18 | + | 12 | X | − | 9 | X | + | 6 | X |
| = | 18 | + | 9 | X |
| 18 | + | 9 | X | = | 128 | − | ( | 30 | − | ( | 7 | + | ( | 5 | − | 2 | ) | ) | ) |
| 方程右边 = | 128 | − | 30 | + | ( | 7 | + | ( | 5 | − | 2 | ) | ) |
| = | 98 | + | ( | 7 | + | ( | 5 | − | 2 | ) | ) |
| = | 98 | + | 7 | + | ( | 5 | − | 2 | ) |
| = | 105 | + | ( | 5 | − | 2 | ) |
| = | 105 | + | 5 | − | 2 |
| = | 108 |
| 18 | + | 9 | X | = | 108 |
| 18 | + | 9 | X | = | 108 |
| 9 | X | = | 108 | − | 18 |
| 9 | X | = | 90 |
| X | = | 90 | ÷ | 9 |
| = | 90 | × | 1 9 |
| = | 10 | × | 1 |
| X | = | 10 |