| ( | 10 | − | X | ) | × | 30 | = | ( | 20 | − | X | ) | × | 10 |
| Left side of the equation = | 10 | × | 30 | − | X | × | 30 |
| = | 300 | − | X | × | 30 |
| 300 | − | 30 | X | = | ( | 20 | − | X | ) | × | 10 |
| Right side of the equation = | 20 | × | 10 | − | X | × | 10 |
| = | 200 | − | X | × | 10 |
| 300 | − | 30 | X | = | 200 | − | 10 | X |
| - | 30 | X | + | 10 | X | = | 200 | − | 300 |
| - | 20 | X | = | 200 | − | 300 |
| - | 20 | X | = | - | 100 |
| 100 | = | 20 | X |
| 20 | X | = | 100 |
| X | = | 100 | ÷ | 20 |
| = | 100 | × | 1 20 |
| = | 5 | × | 1 |
| X | = | 5 |