| ( | 51 | − | x | ) | ÷ | ( | 39 | − | x | ) | = | 4 |
| Multiply both sides of the equation by: | ( | 39 | − | x | ) |
| ( | 51 | − | x | ) | = | 4 | ( | 39 | − | x | ) |
| 51 | − | x | = | 4 | ( | 39 | − | x | ) |
| 51 | − | x | = | 4 | × | 39 | − | 4 | x |
| 51 | − | x | = | 156 | − | 4 | x |
| - | x | + | 4 | x | = | 156 | − | 51 |
| 3 | x | = | 156 | − | 51 |
| 3 | x | = | 105 |
| x | = | 105 | ÷ | 3 |
| = | 105 | × | 1 3 |
| = | 35 | × | 1 |
| x | = | 35 |