| 6 | ( | 4 | x | + | 9 | ) | − | 15 | ( | x | − | 5 | ) | = | 30 | + | 20 | x |
| Left side of the equation = | 6 | × | 4 | x | + | 6 | × | 9 | − | 15 | ( | x | − | 5 | ) |
| = | 24 | x | + | 54 | − | 15 | ( | x | − | 5 | ) |
| = | 24 | x | + | 54 | − | 15 | x | + | 15 | × | 5 |
| = | 24 | x | + | 54 | − | 15 | x | + | 75 |
| = | 9 | x | + | 129 |
| 9 | x | + | 129 | = | 30 | + | 20 | x |
| 9 | x | − | 20 | x | = | 30 | − | 129 |
| - | 11 | x | = | 30 | − | 129 |
| - | 11 | x | = | - | 99 |
| 99 | = | 11 | x |
| 11 | x | = | 99 |
| x | = | 99 | ÷ | 11 |
| = | 99 | × | 1 11 |
| = | 9 | × | 1 |
| x | = | 9 |