| - | 2 | + | 7 | ( | 5 | + | 12 | ( | 4 | + | x | ) | ) | = | 15 | ( | 3 | x | + | 9 | ) |
| Left side of the equation = | - | 2 | + | 7 | × | 5 | + | 7 | × | 12 | ( | 4 | + | x | ) |
| = | - | 2 | + | 35 | + | 84 | ( | 4 | + | x | ) |
| = | 33 | + | 84 | ( | 4 | + | x | ) |
| = | 33 | + | 84 | × | 4 | + | 84 | x |
| = | 33 | + | 336 | + | 84 | x |
| = | 369 | + | 84 | x |
| 369 | + | 84 | x | = | 15 | ( | 3 | x | + | 9 | ) |
| Right side of the equation = | 15 | × | 3 | x | + | 15 | × | 9 |
| = | 45 | x | + | 135 |
| 369 | + | 84 | x | = | 45 | x | + | 135 |
| 84 | x | − | 45 | x | = | 135 | − | 369 |
| 39 | x | = | 135 | − | 369 |
| 39 | x | = | - | 234 |
| x | = | - | 234 | ÷ | 39 |
| = | - | 234 | × | 1 39 |
| = | - | 6 | × | 1 |
| x | = | - | 6 |