| 140 | X | + | 150 | ( | 100 | − | X | ) | = | 0 |
| Left side of the equation = | 140 | X | + | 150 | × | 100 | − | 150 | X |
| = | 140 | X | + | 15000 | − | 150 | X |
| = | - | 10 | X | + | 15000 |
| - | 10 | X | + | 15000 | = | 0 |
| - | 10 | X | = | 0 | − | 15000 |
| - | 10 | X | = | - | 15000 |
| 15000 | = | 10 | X |
| 10 | X | = | 15000 |
| X | = | 15000 | ÷ | 10 |
| = | 15000 | × | 1 10 |
| = | 1500 | × | 1 |
| X | = | 1500 |