| ( | 300 | + | 30 | x | ) | ( | 25 | − | x | − | 6 | ) | = | 6300 |
| 方程左边 = | 300 | ( | 25 | − | x | − | 6 | ) | + | 30 | x | ( | 25 | − | x | − | 6 | ) |
| = | 300 | × | 25 | − | 300 | x | − | 300 | × | 6 | + | 30 | x | ( | 25 | − | x | − | 6 | ) |
| = | 7500 | − | 300 | x | − | 1800 | + | 30 | x | ( | 25 | − | x | − | 6 | ) |
| = | 5700 | − | 300 | x | + | 30 | x | ( | 25 | − | x | − | 6 | ) |
| = | 5700 | − | 300 | x | + | 30 | x | × | 25 | − | 30 | x | x | − | 30 | x | × | 6 |
| = | 5700 | − | 300 | x | + | 750 | x | − | 30 | x | x | − | 180 | x |
| = | 5700 | + | 270 | x | − | 30 | x | x |
| 5700 | + | 270 | x | − | 30 | x | x | = | 6300 |