| ( | 80 | − | x | ) | ( | 160 | − | 2 | x | ) | = | 5280 |
| Left side of the equation = | 80 | ( | 160 | − | 2 | x | ) | − | x | ( | 160 | − | 2 | x | ) |
| = | 80 | × | 160 | − | 80 | × | 2 | x | − | x | ( | 160 | − | 2 | x | ) |
| = | 12800 | − | 160 | x | − | x | ( | 160 | − | 2 | x | ) |
| = | 12800 | − | 160 | x | − | x | × | 160 | + | x | × | 2 | x |
| = | 12800 | − | 320 | x | + | x | × | 2 | x |
| 12800 | − | 320 | x | + | x | × | 2 | x | = | 5280 |