| Q | × | 1 | ( | 240 | − | 200 | ) | − | 120 | − | 400 | × | 5 100 | = | 0 |
| Left side of the equation = | Q | × | 1 | ( | 240 | − | 200 | ) | − | 120 | − | 20 |
| = | Q | × | 1 | ( | 240 | − | 200 | ) | − | 140 |
| Q | × | 1 | ( | 240 | − | 200 | ) | − | 140 | = | 0 |
| Left side of the equation = | Q | × | 1 | × | 240 | − | Q | × | 1 | × | 200 | − | 140 |
| = | Q | × | 240 | − | Q | × | 200 | − | 140 |
| = | 40 | Q | − | 140 |
| 40 | Q | − | 140 | = | 0 |
| 40 | Q | = | 0 | + | 140 |
| 40 | Q | = | 140 |
| Q | = | 140 | ÷ | 40 |
| = | 140 | × | 1 40 |
| = | 7 | × | 1 2 |
| Q | = | 7 2 |
| Q | = | 3.5 |