| 12 | ( | x | − | 15 | − | 10 | ) | = | 4 | ( | x | − | 15 | ) |
| Left side of the equation = | 12 | x | − | 12 | × | 15 | − | 12 | × | 10 |
| = | 12 | x | − | 180 | − | 120 |
| = | 12 | x | − | 300 |
| 12 | x | − | 300 | = | 4 | ( | x | − | 15 | ) |
| Right side of the equation = | 4 | x | − | 4 | × | 15 |
| = | 4 | x | − | 60 |
| 12 | x | − | 300 | = | 4 | x | − | 60 |
| 12 | x | − | 4 | x | = | - | 60 | + | 300 |
| 8 | x | = | - | 60 | + | 300 |
| 8 | x | = | 240 |
| x | = | 240 | ÷ | 8 |
| = | 240 | × | 1 8 |
| = | 30 | × | 1 |
| x | = | 30 |