| ( | 15 | + | x | ) | ( | 800 | − | x | ÷ | 3 | × | 100 | ) | = | 12600 |
| 方程左边 = | 15 | ( | 800 | − | x | ÷ | 3 | × | 100 | ) | + | x | ( | 800 | − | x | ÷ | 3 | × | 100 | ) |
| = | 15 | × | 800 | − | 15 | x | ÷ | 3 | × | 100 | + | x | ( | 800 | − | x | ÷ | 3 | × | 100 | ) |
| = | 12000 | − | 500 | x | + | x | ( | 800 | − | x | ÷ | 3 | × | 100 | ) |
| = | 12000 | − | 500 | x | + | x | × | 800 | − | x | x | ÷ | 3 | × | 100 |
| = | 12000 | − | 500 | x | + | x | × | 800 | − | x | x | × | 100 3 |
| = | 12000 | + | 300 | x | − | x | x | × | 100 3 |
| 12000 | + | 300 | x | − | x | x | × | 100 3 | = | 12600 |