| 90000 | ÷ | ( | X | − | 15 | ) | = | 15000 |
| Multiply both sides of the equation by: | ( | X | − | 15 | ) |
| 90000 | = | 15000 | ( | X | − | 15 | ) |
| 90000 | = | 15000 | X | − | 15000 | × | 15 |
| 90000 | = | 15000 | X | − | 225000 |
| - | 15000 | X | = | - | 225000 | − | 90000 |
| - | 15000 | X | = | - | 315000 |
| 315000 | = | 15000 | X |
| 15000 | X | = | 315000 |
| X | = | 315000 | ÷ | 15000 |
| = | 315000 | × | 1 15000 |
| = | 21 | × | 1 |
| X | = | 21 |