| ( | 30 | − | x | ) | ÷ | 30 | = | 2 | x | ÷ | 40 |
| Left side of the equation = | 30 | × | 1 30 | − | x | × | 1 30 |
| = | 1 | − | x | × | 1 30 |
| 1 | − | 1 30 | x | = | 2 | x | ÷ | 40 |
| Right side of the equation = | 1 20 | x |
| 1 | − | 1 30 | x | = | 1 20 | x |
| - | 1 30 | x | − | 1 20 | x | = | - | 1 |
| - | 1 12 | x | = | - | 1 |
| 1 | = | 1 12 | x |
1 12 | x | = | 1 |
| x | = | 1 | ÷ | 1 12 |
| = | 1 | × | 12 |
| x | = | 12 |