| 90 | x | = | ( | 90 | + | 10 | ) | ( | x | − | 2 | ) |
| Right side of the equation = | 90 | ( | x | − | 2 | ) | + | 10 | ( | x | − | 2 | ) |
| = | 90 | x | − | 90 | × | 2 | + | 10 | ( | x | − | 2 | ) |
| = | 90 | x | − | 180 | + | 10 | ( | x | − | 2 | ) |
| = | 90 | x | − | 180 | + | 10 | x | − | 10 | × | 2 |
| = | 90 | x | − | 180 | + | 10 | x | − | 20 |
| = | 100 | x | − | 200 |
| 90 | x | = | 100 | x | − | 200 |
| 90 | x | − | 100 | x | = | - | 200 |
| - | 10 | x | = | - | 200 |
| 200 | = | 10 | x |
| 10 | x | = | 200 |
| x | = | 200 | ÷ | 10 |
| = | 200 | × | 1 10 |
| = | 20 | × | 1 |
| x | = | 20 |