| ( | x | − | 3 | ) | ( | - | 80 | x | + | 560 | ) | − | 80 | = | 160 |
| Left side of the equation = | x | ( | - | 80 | x | + | 560 | ) | − | 3 | ( | - | 80 | x | + | 560 | ) | − | 80 |
| = | - | x | × | 80 | x | + | x | × | 560 | − | 3 | ( | - | 80 | x | + | 560 | ) | − | 80 |
| = | - | x | × | 80 | x | + | 560 | x | + | 3 | × | 80 | x | − | 3 | × | 560 | − | 80 |
| = | - | x | × | 80 | x | + | 560 | x | + | 240 | x | − | 1680 | − | 80 |
| = | - | x | × | 80 | x | + | 800 | x | − | 1760 |
| - | x | × | 80 | x | + | 800 | x | − | 1760 | = | 160 |