| ( | 380 | X | + | 70 | X | ) | − | ( | 285 | + | 120 | X | ) | = | 0 |
| Left side of the equation = | 380 | X | + | 70 | X | − | ( | 285 | + | 120 | X | ) |
| = | 450 | X | − | ( | 285 | + | 120 | X | ) |
| = | 450 | X | − | 285 | − | 120 | X |
| = | 330 | X | − | 285 |
| 330 | X | − | 285 | = | 0 |
| 330 | X | = | 0 | + | 285 |
| 330 | X | = | 285 |
| X | = | 285 | ÷ | 330 |
| = | 285 | × | 1 330 |
| = | 19 | × | 1 22 |
| X | = | 19 22 |
| X | = | 0.863636 |