| ( | 400 | − | 5 | x | ) | ( | 60 | + | 20 | + | x | − | 60 | ) | = | 4500 |
| 方程左边 = | 400 | ( | 60 | + | 20 | + | x | − | 60 | ) | − | 5 | x | ( | 60 | + | 20 | + | x | − | 60 | ) |
| = | 400 | × | 60 | + | 400 | × | 20 | + | 400 | x | − | 400 | × | 60 | − | 5 | x | ( | 60 | + | 20 | + | x | − | 60 | ) |
| = | 24000 | + | 8000 | + | 400 | x | − | 24000 | − | 5 | x | ( | 60 | + | 20 | + | x | − | 60 | ) |
| = | 8000 | + | 400 | x | − | 5 | x | ( | 60 | + | 20 | + | x | − | 60 | ) |
| = | 8000 | + | 400 | x | − | 5 | x | × | 60 | − | 5 | x | × | 20 | − | 5 | x | x |
| = | 8000 | + | 400 | x | − | 300 | x | − | 100 | x | − | 5 | x | x | + | 300 | x |
| = | 8000 | + | 300 | x | − | 5 | x | x |
| 8000 | + | 300 | x | − | 5 | x | x | = | 4500 |