| 8 | ( | x | − | 5 | ) | + | 12 | ( | x | − | 5 | ) | + | 5 | = | - | 15 |
| 方程左边 = | 8 | x | − | 8 | × | 5 | + | 12 | ( | x | − | 5 | ) | + | 5 |
| = | 8 | x | − | 40 | + | 12 | ( | x | − | 5 | ) | + | 5 |
| = | 8 | x | − | 35 | + | 12 | ( | x | − | 5 | ) |
| = | 8 | x | − | 35 | + | 12 | x | − | 12 | × | 5 |
| = | 8 | x | − | 35 | + | 12 | x | − | 60 |
| = | 20 | x | − | 95 |
| 20 | x | − | 95 | = | - | 15 |
| 20 | x | = | - | 15 | + | 95 |
| 20 | x | = | 80 |
| x | = | 80 | ÷ | 20 |
| = | 80 | × | 1 20 |
| = | 4 | × | 1 |
| x | = | 4 |