| ( | 400 | − | 10 | x | ) | ( | 6 | + | 1 2 | x | ) | + | 40 | x | = | 2775 |
| 方程左边 = | 400 | ( | 6 | + | 1 2 | x | ) | − | 10 | x | ( | 6 | + | 1 2 | x | ) | + | 40 | x |
| = | 400 | × | 6 | + | 400 | × | 1 2 | x | − | 10 | x | ( | 6 | + | 1 2 | x | ) | + | 40 | x |
| = | 2400 | + | 200 | x | − | 10 | x | ( | 6 | + | 1 2 | x | ) | + | 40 | x |
| = | 2400 | + | 240 | x | − | 10 | x | ( | 6 | + | 1 2 | x | ) |
| = | 2400 | + | 240 | x | − | 10 | x | × | 6 | − | 10 | x | × | 1 2 | x |
| = | 2400 | + | 240 | x | − | 60 | x | − | 5 | x | x |
| = | 2400 | + | 180 | x | − | 5 | x | x |
| 2400 | + | 180 | x | − | 5 | x | x | = | 2775 |