| ( | 660 | − | 10 | x | ) | ( | 700 | − | 10 | x | ) | = | 2000 |
| Left side of the equation = | 660 | ( | 700 | − | 10 | x | ) | − | 10 | x | ( | 700 | − | 10 | x | ) |
| = | 660 | × | 700 | − | 660 | × | 10 | x | − | 10 | x | ( | 700 | − | 10 | x | ) |
| = | 462000 | − | 6600 | x | − | 10 | x | ( | 700 | − | 10 | x | ) |
| = | 462000 | − | 6600 | x | − | 10 | x | × | 700 | + | 10 | x | × | 10 | x |
| = | 462000 | − | 6600 | x | − | 7000 | x | + | 100 | x | x |
| = | 462000 | − | 13600 | x | + | 100 | x | x |
| 462000 | − | 13600 | x | + | 100 | x | x | = | 2000 |