| ( | 12 | ÷ | 13 | ) | ( | 9 | − | x | ) | ( | 13 | − | 4 | + | x | ) | = | 72 |
| Left side of the equation = | 12 | ÷ | 13 | × | ( | 9 | − | x | ) | ( | 13 | − | 4 | + | x | ) |
| = | 12 13 | ( | 9 | − | x | ) | ( | 13 | − | 4 | + | x | ) |
| = | 12 13 | × | 9 | ( | 13 | − | 4 | + | x | ) | − | 12 13 | x | ( | 13 | − | 4 | + | x | ) |
| = | 108 13 | ( | 13 | − | 4 | + | x | ) | − | 12 13 | x | ( | 13 | − | 4 | + | x | ) |
| = | 108 13 | × | 13 | − | 108 13 | × | 4 | + | 108 13 | x | − | 12 13 | x | ( | 13 | − | 4 | + | x | ) |
| = | 108 | − | 432 13 | + | 108 13 | x | − | 12 13 | x | ( | 13 | − | 4 | + | x | ) |
| = | 972 13 | + | 108 13 | x | − | 12 13 | x | ( | 13 | − | 4 | + | x | ) |
| = | 972 13 | + | 108 13 | x | − | 12 13 | x | × | 13 | + | 12 13 | x | × | 4 | − | 12 13 | x | x |
| = | 972 13 | + | 108 13 | x | − | 12 | x | + | 48 13 | x | − | 12 13 | x | x |
| = | 972 13 | − | 0 | x | − | 12 13 | x | x |
972 13 | − | 0 | x | − | 12 13 | x | x | = | 72 |