| 9 | − | x | ÷ | 50 | + | x | ÷ | 80 | = | 81 | ÷ | 90 |
| Left side of the equation = | 9 | − | 3 400 | x |
| 9 | − | 3 400 | x | = | 81 | ÷ | 90 |
| Right side of the equation = | 9 10 |
| 9 | − | 3 400 | x | = | 9 10 |
| - | 3 400 | x | = | 9 10 | − | 9 |
| - | 3 400 | x | = | - | 81 10 |
81 10 | = | 3 400 | x |
3 400 | x | = | 81 10 |
| x | = | 81 10 | ÷ | 3 400 |
| = | 81 10 | × | 400 3 |
| = | 27 | × | 40 |
| x | = | 1080 |