| ( | 6 | X | + | 5 | ) | + | ( | 4 | X | − | 2 | ) | = | ( | 8 | X | + | 21 | ) |
| Left side of the equation = | 6 | X | + | 5 | + | ( | 4 | X | − | 2 | ) |
| = | 6 | X | + | 5 | + | 4 | X | − | 2 |
| = | 10 | X | + | 3 |
| 10 | X | + | 3 | = | ( | 8 | X | + | 21 | ) |
| Right side of the equation = | 8 | X | + | 21 |
| 10 | X | + | 3 | = | 8 | X | + | 21 |
| 10 | X | − | 8 | X | = | 21 | − | 3 |
| 2 | X | = | 21 | − | 3 |
| 2 | X | = | 18 |
| X | = | 18 | ÷ | 2 |
| = | 18 | × | 1 2 |
| = | 9 | × | 1 |
| X | = | 9 |