| 90 | − | x | = | 1 | ÷ | 4 | × | ( | 180 | − | x | ) |
| 方程右边 = | 1 4 | ( | 180 | − | x | ) |
| 90 | − | x | = | 1 4 | ( | 180 | − | x | ) |
| 方程右边 = | 1 4 | × | 180 | − | 1 4 | x |
| = | 45 | − | 1 4 | x |
| 90 | − | x | = | 45 | − | 1 4 | x |
| - | x | + | 1 4 | x | = | 45 | − | 90 |
| - | 3 4 | x | = | 45 | − | 90 |
| - | 3 4 | x | = | - | 45 |
| 45 | = | 3 4 | x |
3 4 | x | = | 45 |
| x | = | 45 | ÷ | 3 4 |
| = | 45 | × | 4 3 |
| = | 15 | × | 4 |
| x | = | 60 |