| ( | 49 | − | N | ) | = | ( | N | − | 40 | ) | ÷ | 2 |
| Left side of the equation = | 49 | − | N |
| 49 | − | N | = | ( | N | − | 40 | ) | ÷ | 2 |
| Right side of the equation = | N | × | 1 2 | − | 40 | × | 1 2 |
| = | N | × | 1 2 | − | 20 |
| 49 | − | N | = | 1 2 | N | − | 20 |
| - | N | − | 1 2 | N | = | - | 20 | − | 49 |
| - | 3 2 | N | = | - | 20 | − | 49 |
| - | 3 2 | N | = | - | 69 |
| 69 | = | 3 2 | N |
3 2 | N | = | 69 |
| N | = | 69 | ÷ | 3 2 |
| = | 69 | × | 2 3 |
| = | 23 | × | 2 |
| N | = | 46 |