| ( | 160 | + | 2 | x | ) | ( | 20 | − | x | ) | = | 1800 |
| Left side of the equation = | 160 | ( | 20 | − | x | ) | + | 2 | x | ( | 20 | − | x | ) |
| = | 160 | × | 20 | − | 160 | x | + | 2 | x | ( | 20 | − | x | ) |
| = | 3200 | − | 160 | x | + | 2 | x | ( | 20 | − | x | ) |
| = | 3200 | − | 160 | x | + | 2 | x | × | 20 | − | 2 | x | x |
| = | 3200 | − | 160 | x | + | 40 | x | − | 2 | x | x |
| = | 3200 | − | 120 | x | − | 2 | x | x |
| 3200 | − | 120 | x | − | 2 | x | x | = | 1800 |