| 54 | × | 100 | ÷ | X | ÷ | 21 20 | ÷ | 90 | × | 100 | = | 78 |
| Multiply both sides of the equation by: | X |
| 54 | × | 100 | ÷ | 21 20 | ÷ | 90 | × | 100 | = | 78 | X |
| - | 78 | X | = | - | 54 | × | 100 | ÷ | 21 20 | ÷ | 90 | × | 100 |
| - | 78 | X | = | - | 40000 7 |
40000 7 | = | 78 | X |
| 78 | X | = | 40000 7 |
| X | = | 40000 7 | ÷ | 78 |
| = | 40000 7 | × | 1 78 |
| = | 20000 7 | × | 1 39 |
| X | = | 20000 273 |
| X | = | 73.260073 |