| 300 | x | + | 390 | ( | 30 | − | x | ) | = | 17700 |
| Left side of the equation = | 300 | x | + | 390 | × | 30 | − | 390 | x |
| = | 300 | x | + | 11700 | − | 390 | x |
| = | - | 90 | x | + | 11700 |
| - | 90 | x | + | 11700 | = | 17700 |
| - | 90 | x | = | 17700 | − | 11700 |
| - | 90 | x | = | 6000 |
| - | 6000 | = | 90 | x |
| 90 | x | = | - | 6000 |
| x | = | - | 6000 | ÷ | 90 |
| = | - | 6000 | × | 1 90 |
| = | - | 200 | × | 1 3 |
| x | = | - | 200 3 |
| x | = | - 66.666667 |