| ( | 20 | − | x | ) | ( | 1500 | − | 20 | x | ) | = | 6080 |
| Left side of the equation = | 20 | ( | 1500 | − | 20 | x | ) | − | x | ( | 1500 | − | 20 | x | ) |
| = | 20 | × | 1500 | − | 20 | × | 20 | x | − | x | ( | 1500 | − | 20 | x | ) |
| = | 30000 | − | 400 | x | − | x | ( | 1500 | − | 20 | x | ) |
| = | 30000 | − | 400 | x | − | x | × | 1500 | + | x | × | 20 | x |
| = | 30000 | − | 1900 | x | + | x | × | 20 | x |
| 30000 | − | 1900 | x | + | x | × | 20 | x | = | 6080 |