| 12 | ( | x | + | 6 | ) | + | 6 | ( | 12 | + | x | ) | = | 234 |
| Left side of the equation = | 12 | x | + | 12 | × | 6 | + | 6 | ( | 12 | + | x | ) |
| = | 12 | x | + | 72 | + | 6 | ( | 12 | + | x | ) |
| = | 12 | x | + | 72 | + | 6 | × | 12 | + | 6 | x |
| = | 12 | x | + | 72 | + | 72 | + | 6 | x |
| = | 18 | x | + | 144 |
| 18 | x | + | 144 | = | 234 |
| 18 | x | = | 234 | − | 144 |
| 18 | x | = | 90 |
| x | = | 90 | ÷ | 18 |
| = | 90 | × | 1 18 |
| = | 5 | × | 1 |
| x | = | 5 |