| ( | 500 | − | 10 | X | ) | ( | 10 | + | X | ) | = | 8000 |
| Left side of the equation = | 500 | ( | 10 | + | X | ) | − | 10 | X | ( | 10 | + | X | ) |
| = | 500 | × | 10 | + | 500 | X | − | 10 | X | ( | 10 | + | X | ) |
| = | 5000 | + | 500 | X | − | 10 | X | ( | 10 | + | X | ) |
| = | 5000 | + | 500 | X | − | 10 | X | × | 10 | − | 10 | X | X |
| = | 5000 | + | 500 | X | − | 100 | X | − | 10 | X | X |
| = | 5000 | + | 400 | X | − | 10 | X | X |
| 5000 | + | 400 | X | − | 10 | X | X | = | 8000 |