| ( | 390 | − | X | ) | ÷ | X | = | - | 89 1000 |
| Multiply both sides of the equation by: | X |
| ( | 390 | − | X | ) | = | - | 89 1000 | X |
| 390 | − | X | = | - | 89 1000 | X |
| - | X | + | 89 1000 | X | = | - | 390 |
| - | 911 1000 | X | = | - | 390 |
| 390 | = | 911 1000 | X |
911 1000 | X | = | 390 |
| X | = | 390 | ÷ | 911 1000 |
| = | 390 | × | 1000 911 |
| X | = | 390000 911 |
| X | = | 428.100988 |