| 11 | x | + | 9 | ( | x | + | 31 | ) | = | 30 | x | − | 221 |
| Left side of the equation = | 11 | x | + | 9 | x | + | 9 | × | 31 |
| = | 11 | x | + | 9 | x | + | 279 |
| = | 20 | x | + | 279 |
| 20 | x | + | 279 | = | 30 | x | − | 221 |
| 20 | x | − | 30 | x | = | - | 221 | − | 279 |
| - | 10 | x | = | - | 221 | − | 279 |
| - | 10 | x | = | - | 500 |
| 500 | = | 10 | x |
| 10 | x | = | 500 |
| x | = | 500 | ÷ | 10 |
| = | 500 | × | 1 10 |
| = | 50 | × | 1 |
| x | = | 50 |