| 120000 | ÷ | ( | 100000 | − | X | ) | = | 15 2 |
| Multiply both sides of the equation by: | ( | 100000 | − | X | ) |
| 120000 | = | 15 2 | ( | 100000 | − | X | ) |
| 120000 | = | 15 2 | × | 100000 | − | 15 2 | X |
| 120000 | = | 750000 | − | 15 2 | X |
15 2 | X | = | 750000 | − | 120000 |
15 2 | X | = | 630000 |
| X | = | 630000 | ÷ | 15 2 |
| = | 630000 | × | 2 15 |
| = | 42000 | × | 2 |
| X | = | 84000 |