| ( | X | − | 50 | ) | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) | = | 12000 |
| 方程左边 = | X | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) | − | 50 | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) |
| = | X | × | 800 | − | X | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | − | 50 | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) |
| = | X | × | 800 | − | X | ( | X | − | 60 | ) | × | 20 | − | 50 | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) |
| = | 800 | X | − | X | X | × | 20 | + | X | × | 60 | × | 20 | − | 50 | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) |
| = | 800 | X | − | X | X | × | 20 | + | X | × | 1200 | − | 50 | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) |
| = | 2000 | X | − | X | X | × | 20 | − | 50 | ( | 800 | − | ( | X | − | 60 | ) | ÷ | 5 | × | 100 | ) |
| = | 2000 | X | − | X | X | × | 20 | − | 50 | × | 800 | + | 50 | ( | X | − | 60 | ) | ÷ | 5 | × | 100 |
| = | 2000 | X | − | X | X | × | 20 | − | 40000 | + | 1000 | ( | X | − | 60 | ) |
| = | 2000 | X | − | X | X | × | 20 | − | 40000 | + | 1000 | X | − | 1000 | × | 60 |
| = | 2000 | X | − | X | X | × | 20 | − | 40000 | + | 1000 | X | − | 60000 |
| = | 3000 | X | − | X | X | × | 20 | − | 100000 |
| 3000 | X | − | X | X | × | 20 | − | 100000 | = | 12000 |