| ( | x | − | 6 | ) | ( | 400 | − | 20 | x | + | 160 | ) | = | 2240 |
| Left side of the equation = | x | ( | 400 | − | 20 | x | + | 160 | ) | − | 6 | ( | 400 | − | 20 | x | + | 160 | ) |
| = | x | × | 400 | − | x | × | 20 | x | + | x | × | 160 | − | 6 | ( | 400 | − | 20 | x | + | 160 | ) |
| = | 560 | x | − | x | × | 20 | x | − | 6 | ( | 400 | − | 20 | x | + | 160 | ) |
| = | 560 | x | − | x | × | 20 | x | − | 6 | × | 400 | + | 6 | × | 20 | x | − | 6 | × | 160 |
| = | 560 | x | − | x | × | 20 | x | − | 2400 | + | 120 | x | − | 960 |
| = | 680 | x | − | x | × | 20 | x | − | 3360 |
| 680 | x | − | x | × | 20 | x | − | 3360 | = | 2240 |