| 6000 | + | ( | 200 | + | 10 | x | ) | ( | 30 | − | x | ) | + | 40 | ( | 400 | − | 10 | x | ) | = | 9000 |
| 方程左边 = | 6000 | + | 200 | ( | 30 | − | x | ) | + | 10 | x | ( | 30 | − | x | ) | + | 40 | ( | 400 | − | 10 | x | ) |
| = | 6000 | + | 200 | × | 30 | − | 200 | x | + | 10 | x | ( | 30 | − | x | ) | + | 40 | ( | 400 | − | 10 | x | ) |
| = | 6000 | + | 6000 | − | 200 | x | + | 10 | x | ( | 30 | − | x | ) | + | 40 | ( | 400 | − | 10 | x | ) |
| = | 12000 | − | 200 | x | + | 10 | x | ( | 30 | − | x | ) | + | 40 | ( | 400 | − | 10 | x | ) |
| = | 12000 | − | 200 | x | + | 10 | x | × | 30 | − | 10 | x | x | + | 40 | ( | 400 | − | 10 | x | ) |
| = | 12000 | − | 200 | x | + | 300 | x | − | 10 | x | x | + | 40 | ( | 400 | − | 10 | x | ) |
| = | 12000 | + | 100 | x | − | 10 | x | x | + | 40 | ( | 400 | − | 10 | x | ) |
| = | 12000 | + | 100 | x | − | 10 | x | x | + | 40 | × | 400 | − | 40 | × | 10 | x |
| = | 12000 | + | 100 | x | − | 10 | x | x | + | 16000 | − | 400 | x |
| = | 28000 | − | 300 | x | − | 10 | x | x |
| 28000 | − | 300 | x | − | 10 | x | x | = | 9000 |