| 90 | − | x | = | 3 | ÷ | 1 | × | ( | 180 | − | x | ) | − | 20 |
| Right side of the equation = | 3 | ( | 180 | − | x | ) | − | 20 |
| 90 | − | x | = | 3 | ( | 180 | − | x | ) | − | 20 |
| Right side of the equation = | 3 | × | 180 | − | 3 | x | − | 20 |
| = | 540 | − | 3 | x | − | 20 |
| = | 520 | − | 3 | x |
| 90 | − | x | = | 520 | − | 3 | x |
| - | x | + | 3 | x | = | 520 | − | 90 |
| 2 | x | = | 520 | − | 90 |
| 2 | x | = | 430 |
| x | = | 430 | ÷ | 2 |
| = | 430 | × | 1 2 |
| = | 215 | × | 1 |
| x | = | 215 |