| ( | - | 5 | x | + | 500 | ) | ( | x | − | 40 | ) | = | 4000 |
| Left side of the equation = | - | 5 | x | ( | x | − | 40 | ) | + | 500 | ( | x | − | 40 | ) |
| = | - | 5 | x | x | + | 5 | x | × | 40 | + | 500 | ( | x | − | 40 | ) |
| = | - | 5 | x | x | + | 200 | x | + | 500 | ( | x | − | 40 | ) |
| = | - | 5 | x | x | + | 200 | x | + | 500 | x | − | 500 | × | 40 |
| = | - | 5 | x | x | + | 200 | x | + | 500 | x | − | 20000 |
| = | - | 5 | x | x | + | 700 | x | − | 20000 |
| - | 5 | x | x | + | 700 | x | − | 20000 | = | 4000 |