| 90 | = | ( | 411 | + | ( | 100 | x | ) | ) | ÷ | ( | 6 | + | x | ) |
| Multiply both sides of the equation by: | ( | 6 | + | x | ) |
| 90 | ( | 6 | + | x | ) | = | ( | 411 | + | ( | 100 | x | ) | ) |
| 90 | × | 6 | + | 90 | x | = | ( | 411 | + | ( | 100 | x | ) | ) |
| 90 | × | 6 | + | 90 | x | = | 411 | + | ( | 100 | x | ) |
| 540 | + | 90 | x | = | 411 | + | ( | 100 | x | ) |
| 540 | + | 90 | x | = | 411 | + | 100 | x |
| 90 | x | − | 100 | x | = | 411 | − | 540 |
| - | 10 | x | = | 411 | − | 540 |
| - | 10 | x | = | - | 129 |
| 129 | = | 10 | x |
| 10 | x | = | 129 |
| x | = | 129 | ÷ | 10 |
| = | 129 | × | 1 10 |
| x | = | 129 10 |
| x | = | 12.9 |