| 7 | ( | 7 | ÷ | 12 | × | x | − | 13 | ) | − | 5 | ( | 5 | ÷ | 12 | × | x | + | 13 | ) | = | 20 |
| Left side of the equation = | 7 | × | 7 | ÷ | 12 | × | x | − | 7 | × | 13 | − | 5 | ( | 5 | ÷ | 12 | × | x | + | 13 | ) |
| = | 49 12 | x | − | 91 | − | 5 | ( | 5 | ÷ | 12 | × | x | + | 13 | ) |
| = | 49 12 | x | − | 91 | − | 5 | × | 5 | ÷ | 12 | × | x | − | 5 | × | 13 |
| = | 49 12 | x | − | 91 | − | 25 12 | x | − | 65 |
| = | 2 | x | − | 156 |
| 2 | x | − | 156 | = | 20 |
| 2 | x | = | 20 | + | 156 |
| 2 | x | = | 176 |
| x | = | 176 | ÷ | 2 |
| = | 176 | × | 1 2 |
| = | 88 | × | 1 |
| x | = | 88 |