| 30 | x | + | 40 | ( | 360 | − | x | ) | = | 12000 |
| Left side of the equation = | 30 | x | + | 40 | × | 360 | − | 40 | x |
| = | 30 | x | + | 14400 | − | 40 | x |
| = | - | 10 | x | + | 14400 |
| - | 10 | x | + | 14400 | = | 12000 |
| - | 10 | x | = | 12000 | − | 14400 |
| - | 10 | x | = | - | 2400 |
| 2400 | = | 10 | x |
| 10 | x | = | 2400 |
| x | = | 2400 | ÷ | 10 |
| = | 2400 | × | 1 10 |
| = | 240 | × | 1 |
| x | = | 240 |