| ( | N | − | 80 | ) | ÷ | ( | - | 20 | − | 80 | ) | = | 68 500 |
| Multiply both sides of the equation by: | ( | - | 20 | − | 80 | ) |
| ( | N | − | 80 | ) | = | 68 500 | ( | - | 20 | − | 80 | ) |
| N | − | 80 | = | 68 500 | ( | - | 20 | − | 80 | ) |
| N | − | 80 | = | - | 68 500 | × | 20 | − | 68 500 | × | 80 |
| N | − | 80 | = | - | 68 25 | − | 272 25 |
| N | − | 80 | = | - | 68 5 |
| N | = | - | 68 5 | + | 80 |
| N | = | 332 5 |