| x | = | ( | 21 | ÷ | 5 | ) | ÷ | ( | - | ( | 49 | ÷ | 40 | ) | ) |
| Multiply both sides of the equation by: | ( | - | ( | 49 | ÷ | 40 | ) | ) |
| x | ( | - | ( | 49 | ÷ | 40 | ) | ) | = | ( | 21 | ÷ | 5 | ) |
| - | x | ( | 49 | ÷ | 40 | ) | = | ( | 21 | ÷ | 5 | ) |
| - | x | ( | 49 | ÷ | 40 | ) | = | 21 | ÷ | 5 |
| - | x | ( | 49 | ÷ | 40 | ) | = | 21 5 |
| - | x | × | 49 | ÷ | 40 | = | 21 5 |
| - | x | × | 49 40 | = | 21 5 |
| - | 21 5 | = | 49 40 | x |
49 40 | x | = | - | 21 5 |
| x | = | - | 21 5 | ÷ | 49 40 |
| = | - | 21 5 | × | 40 49 |
| = | - | 3 | × | 8 7 |
| x | = | - | 24 7 |
| x | = | - 3.428571 |