| ( | 300 | + | X | ) | ÷ | 12 | = | ( | 100 | + | X | ) | ÷ | 7 |
| Left side of the equation = | 300 | × | 1 12 | + | X | × | 1 12 |
| = | 25 | + | X | × | 1 12 |
| 25 | + | 1 12 | X | = | ( | 100 | + | X | ) | ÷ | 7 |
| Right side of the equation = | 100 | × | 1 7 | + | X | × | 1 7 |
| = | 100 7 | + | X | × | 1 7 |
| 25 | + | 1 12 | X | = | 100 7 | + | 1 7 | X |
1 12 | X | − | 1 7 | X | = | 100 7 | − | 25 |
| - | 5 84 | X | = | 100 7 | − | 25 |
| - | 5 84 | X | = | - | 75 7 |
75 7 | = | 5 84 | X |
5 84 | X | = | 75 7 |
| X | = | 75 7 | ÷ | 5 84 |
| = | 75 7 | × | 84 5 |
| = | 15 | × | 12 |
| X | = | 180 |