| ( | 3 4 | ( | x | − | 80 | ) | ) | ÷ | 4200 | = | ( | ( | x | − | 160 | ) | × | 3 4 | ) | ÷ | 4000 |
| 方程左边 = | 3 4 | ( | x | − | 80 | ) | × | 1 4200 |
| = | 1 5600 | ( | x | − | 80 | ) |
| = | 1 5600 | x | − | 1 5600 | × | 80 |
| = | 1 5600 | x | − | 1 70 |
1 5600 | x | − | 1 70 | = | ( | ( | x | − | 160 | ) | × | 3 4 | ) | ÷ | 4000 |
| 方程右边 = | ( | x | − | 160 | ) | × | 3 4 | × | 1 4000 |
| = | ( | x | − | 160 | ) | × | 3 16000 |
| = | x | × | 3 16000 | − | 160 | × | 3 16000 |
| = | x | × | 3 16000 | − | 3 100 |
1 5600 | x | − | 1 70 | = | 3 16000 | x | − | 3 100 |
1 5600 | x | − | 3 16000 | x | = | - | 3 100 | + | 1 70 |
| - | 1 112000 | x | = | - | 3 100 | + | 1 70 |
| - | 1 112000 | x | = | - | 11 700 |
11 700 | = | 1 112000 | x |
1 112000 | x | = | 11 700 |
| x | = | 11 700 | ÷ | 1 112000 |
| = | 11 700 | × | 112000 |
| = | 11 | × | 160 |
| x | = | 1760 |