| ( | 166 | − | x | ) | ÷ | x | × | 100 | = | 90 |
| Multiply both sides of the equation by: | x |
| ( | 166 | − | x | ) | × | 100 | = | 90 | x |
| 166 | × | 100 | − | x | × | 100 | = | 90 | x |
| 16600 | − | x | × | 100 | = | 90 | x |
| - | 100 | x | − | 90 | x | = | - | 16600 |
| - | 190 | x | = | - | 16600 |
| 16600 | = | 190 | x |
| 190 | x | = | 16600 |
| x | = | 16600 | ÷ | 190 |
| = | 16600 | × | 1 190 |
| = | 1660 | × | 1 19 |
| x | = | 1660 19 |
| x | = | 87.368421 |