| 90 | ÷ | 6 | − | x | = | x | − | 90 | ÷ | ( | 6 | + | 4 | ) |
| Multiply both sides of the equation by: | ( | 6 | + | 4 | ) |
| 90 | ÷ | 6 | × | ( | 6 | + | 4 | ) | − | x | ( | 6 | + | 4 | ) | = | x | ( | 6 | + | 4 | ) | − | 90 |
| 90 | ÷ | 6 | × | 6 | + | 90 | ÷ | 6 | × | 4 | − | x | ( | 6 | + | 4 | ) | = | x | ( | 6 | + | 4 | ) | − | 90 |
| 90 | ÷ | 6 | × | 6 | + | 90 | ÷ | 6 | × | 4 | − | x | ( | 6 | + | 4 | ) | = | x | × | 6 | + | x | × | 4 | − | 90 |
| 90 | + | 60 | − | x | ( | 6 | + | 4 | ) | = | x | × | 6 | + | x | × | 4 | − | 90 |
| 150 | − | x | ( | 6 | + | 4 | ) | = | 10 | x | − | 90 |
| 150 | − | x | × | 6 | − | x | × | 4 | = | 10 | x | − | 90 |
| 150 | − | 10 | x | = | 10 | x | − | 90 |
| - | 10 | x | − | 10 | x | = | - | 90 | − | 150 |
| - | 20 | x | = | - | 90 | − | 150 |
| - | 20 | x | = | - | 240 |
| 240 | = | 20 | x |
| 20 | x | = | 240 |
| x | = | 240 | ÷ | 20 |
| = | 240 | × | 1 20 |
| = | 12 | × | 1 |
| x | = | 12 |