| ( | x | − | 80 | ) | ( | 680 | − | 2 | x | ) | = | 33000 |
| Left side of the equation = | x | ( | 680 | − | 2 | x | ) | − | 80 | ( | 680 | − | 2 | x | ) |
| = | x | × | 680 | − | x | × | 2 | x | − | 80 | ( | 680 | − | 2 | x | ) |
| = | 680 | x | − | x | × | 2 | x | − | 80 | × | 680 | + | 80 | × | 2 | x |
| = | 680 | x | − | x | × | 2 | x | − | 54400 | + | 160 | x |
| = | 840 | x | − | x | × | 2 | x | − | 54400 |
| 840 | x | − | x | × | 2 | x | − | 54400 | = | 33000 |