| 90 | ( | 3 | − | x | ) | = | 45 | ( | 5 | − | x | ) |
| Left side of the equation = | 90 | × | 3 | − | 90 | x |
| = | 270 | − | 90 | x |
| 270 | − | 90 | x | = | 45 | ( | 5 | − | x | ) |
| Right side of the equation = | 45 | × | 5 | − | 45 | x |
| = | 225 | − | 45 | x |
| 270 | − | 90 | x | = | 225 | − | 45 | x |
| - | 90 | x | + | 45 | x | = | 225 | − | 270 |
| - | 45 | x | = | 225 | − | 270 |
| - | 45 | x | = | - | 45 |
| 45 | = | 45 | x |
| 45 | x | = | 45 |
| x | = | 45 | ÷ | 45 |
| = | 45 | × | 1 45 |
| = | 1 | × | 1 |
| x | = | 1 |