| ( | 150 | − | x | ) | ( | 20 | + | 4 | x | ) | − | 50 | = | 2750 |
| 方程左边 = | 150 | ( | 20 | + | 4 | x | ) | − | x | ( | 20 | + | 4 | x | ) | − | 50 |
| = | 150 | × | 20 | + | 150 | × | 4 | x | − | x | ( | 20 | + | 4 | x | ) | − | 50 |
| = | 3000 | + | 600 | x | − | x | ( | 20 | + | 4 | x | ) | − | 50 |
| = | 2950 | + | 600 | x | − | x | ( | 20 | + | 4 | x | ) |
| = | 2950 | + | 600 | x | − | x | × | 20 | − | x | × | 4 | x |
| = | 2950 | + | 580 | x | − | x | × | 4 | x |
| 2950 | + | 580 | x | − | x | × | 4 | x | = | 2750 |