| 12 | ( | 13 | − | 4 | + | x | ÷ | 13 | ) | ( | 9 | + | x | ) | ÷ | 2 | = | 36 |
| Left side of the equation = | 6 | ( | 13 | − | 4 | + | x | ÷ | 13 | ) | ( | 9 | + | x | ) |
| 6 | ( | 13 | − | 4 | + | x | ÷ | 13 | ) | ( | 9 | + | x | ) | = | 36 |
| Left side of the equation = | 6 | × | 13 | ( | 9 | + | x | ) | − | 6 | × | 4 | ( | 9 | + | x | ) | + | 6 | x | ÷ | 13 | × | ( | 9 | + | x | ) |
| = | 78 | ( | 9 | + | x | ) | − | 24 | ( | 9 | + | x | ) | + | 6 13 | x | ( | 9 | + | x | ) |
| = | 78 | × | 9 | + | 78 | x | − | 24 | ( | 9 | + | x | ) | + | 6 13 | x | ( | 9 | + | x | ) |
| = | 702 | + | 78 | x | − | 24 | ( | 9 | + | x | ) | + | 6 13 | x | ( | 9 | + | x | ) |
| = | 702 | + | 78 | x | − | 24 | × | 9 | − | 24 | x | + | 6 13 | x | ( | 9 | + | x | ) |
| = | 702 | + | 78 | x | − | 216 | − | 24 | x | + | 6 13 | x | ( | 9 | + | x | ) |
| = | 486 | + | 54 | x | + | 6 13 | x | ( | 9 | + | x | ) |
| = | 486 | + | 54 | x | + | 6 13 | x | × | 9 | + | 6 13 | x | x |
| = | 486 | + | 54 | x | + | 54 13 | x | + | 6 13 | x | x |
| = | 486 | + | 756 13 | x | + | 6 13 | x | x |
| 486 | + | 756 13 | x | + | 6 13 | x | x | = | 36 |