| ( | 1800 | − | 1000 | − | x | ) | ( | 4 | + | x | ÷ | 50 | ) | = | 4200 |
| 方程左边 = | 1800 | ( | 4 | + | x | ÷ | 50 | ) | − | 1000 | ( | 4 | + | x | ÷ | 50 | ) | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 1800 | × | 4 | + | 1800 | x | ÷ | 50 | − | 1000 | ( | 4 | + | x | ÷ | 50 | ) | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 7200 | + | 36 | x | − | 1000 | ( | 4 | + | x | ÷ | 50 | ) | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 7200 | + | 36 | x | − | 1000 | × | 4 | − | 1000 | x | ÷ | 50 | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 7200 | + | 36 | x | − | 4000 | − | 20 | x | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 3200 | + | 16 | x | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 3200 | + | 16 | x | − | x | × | 4 | − | x | x | ÷ | 50 |
| = | 3200 | + | 12 | x | − | x | x | × | 1 50 |
| 3200 | + | 12 | x | − | x | x | × | 1 50 | = | 4200 |