| 50 | × | 120 100 | x | + | ( | ( | 120 100 | x | ) | − | 30 | ) | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 | = | 660 |
| 方程左边 = | 60 | x | + | ( | ( | 120 100 | x | ) | − | 30 | ) | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 |
| 60 | x | + | ( | ( | 120 100 | x | ) | − | 30 | ) | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 | = | 660 |
| 方程左边 = | 60 | x | + | ( | 120 100 | x | ) | ( | x | ÷ | 4800 | − | 50 | ) | − | 30 | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 |
| = | 60 | x | + | 120 100 | x | ( | x | ÷ | 4800 | − | 50 | ) | − | 30 | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 |
| = | 60 | x | + | 120 100 | x | x | ÷ | 4800 | − | 120 100 | x | × | 50 | − | 30 | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 |
| = | 60 | x | + | 1 4000 | x | x | − | 60 | x | − | 30 | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 |
| = | 0 | x | + | 1 4000 | x | x | − | 30 | ( | x | ÷ | 4800 | − | 50 | ) | − | 4800 |
| = | 1 4000 | x | x | − | 30 | x | ÷ | 4800 | + | 30 | × | 50 | − | 4800 |
| = | 1 4000 | x | x | − | 1 160 | x | + | 1500 | − | 4800 |
| = | 1 4000 | x | x | − | 1 160 | x | − | 3300 |
1 4000 | x | x | − | 1 160 | x | − | 3300 | = | 660 |