| 0 | = | ( | Q | − | 560 | − | 120 | ) | × | 10 | − | 1200 |
| Right side of the equation = | Q | × | 10 | − | 560 | × | 10 | − | 120 | × | 10 | − | 1200 |
| = | Q | × | 10 | − | 5600 | − | 1200 | − | 1200 |
| = | 10 | Q | − | 8000 |
| 0 | = | 10 | Q | − | 8000 |
| - | 10 | Q | = | - | 8000 | − | 0 |
| - | 10 | Q | = | - | 8000 |
| 8000 | = | 10 | Q |
| 10 | Q | = | 8000 |
| Q | = | 8000 | ÷ | 10 |
| = | 8000 | × | 1 10 |
| = | 800 | × | 1 |
| Q | = | 800 |