| ( | 1500 | − | 20 | x | ) | ( | x | − | 40 | ) | = | 6080 |
| Left side of the equation = | 1500 | ( | x | − | 40 | ) | − | 20 | x | ( | x | − | 40 | ) |
| = | 1500 | x | − | 1500 | × | 40 | − | 20 | x | ( | x | − | 40 | ) |
| = | 1500 | x | − | 60000 | − | 20 | x | ( | x | − | 40 | ) |
| = | 1500 | x | − | 60000 | − | 20 | x | x | + | 20 | x | × | 40 |
| = | 1500 | x | − | 60000 | − | 20 | x | x | + | 800 | x |
| = | 2300 | x | − | 60000 | − | 20 | x | x |
| 2300 | x | − | 60000 | − | 20 | x | x | = | 6080 |