| ( | 100 | − | X | ) | × | 40000 | − | 400000 | = | 0 |
| Left side of the equation = | 100 | × | 40000 | − | X | × | 40000 | − | 400000 |
| = | 4000000 | − | X | × | 40000 | − | 400000 |
| = | 3600000 | − | 40000 | X |
| 3600000 | − | 40000 | X | = | 0 |
| - | 40000 | X | = | 0 | − | 3600000 |
| - | 40000 | X | = | - | 3600000 |
| 3600000 | = | 40000 | X |
| 40000 | X | = | 3600000 |
| X | = | 3600000 | ÷ | 40000 |
| = | 3600000 | × | 1 40000 |
| = | 90 | × | 1 |
| X | = | 90 |