| 60 | n | + | 12000 | = | 90 | ( | n | − | 2 | ) |
| Right side of the equation = | 90 | n | − | 90 | × | 2 |
| = | 90 | n | − | 180 |
| 60 | n | + | 12000 | = | 90 | n | − | 180 |
| 60 | n | − | 90 | n | = | - | 180 | − | 12000 |
| - | 30 | n | = | - | 180 | − | 12000 |
| - | 30 | n | = | - | 12180 |
| 12180 | = | 30 | n |
| 30 | n | = | 12180 |
| n | = | 12180 | ÷ | 30 |
| = | 12180 | × | 1 30 |
| = | 406 | × | 1 |
| n | = | 406 |