| ( | X | + | 1 | ) | × | 6 | = | ( | X | − | 1 | ) | × | 9 |
| Left side of the equation = | X | × | 6 | + | 1 | × | 6 |
| = | X | × | 6 | + | 6 |
| 6 | X | + | 6 | = | ( | X | − | 1 | ) | × | 9 |
| Right side of the equation = | X | × | 9 | − | 1 | × | 9 |
| = | X | × | 9 | − | 9 |
| 6 | X | + | 6 | = | 9 | X | − | 9 |
| 6 | X | − | 9 | X | = | - | 9 | − | 6 |
| - | 3 | X | = | - | 9 | − | 6 |
| - | 3 | X | = | - | 15 |
| 15 | = | 3 | X |
| 3 | X | = | 15 |
| X | = | 15 | ÷ | 3 |
| = | 15 | × | 1 3 |
| = | 5 | × | 1 |
| X | = | 5 |