| x | + | 2 | x | + | ( | x | + | 9 | ) | + | ( | x | + | 9 | − | 25 | ) | = | 173 |
| Left side of the equation = | 3 | x | + | ( | x | + | 9 | ) | + | ( | x | + | 9 | − | 25 | ) |
| 3 | x | + | ( | x | + | 9 | ) | + | ( | x | + | 9 | − | 25 | ) | = | 173 |
| Left side of the equation = | 3 | x | + | x | + | 9 | + | ( | x | + | 9 | − | 25 | ) |
| = | 4 | x | + | 9 | + | ( | x | + | 9 | − | 25 | ) |
| = | 4 | x | + | 9 | + | x | + | 9 | − | 25 |
| = | 5 | x | − | 7 |
| 5 | x | − | 7 | = | 173 |
| 5 | x | = | 173 | + | 7 |
| 5 | x | = | 180 |
| x | = | 180 | ÷ | 5 |
| = | 180 | × | 1 5 |
| = | 36 | × | 1 |
| x | = | 36 |