| ( | x | + | 51 | ) | ÷ | ( | x | + | 78 | ) | = | 4 5 |
| Multiply both sides of the equation by: | ( | x | + | 78 | ) |
| ( | x | + | 51 | ) | = | 4 5 | ( | x | + | 78 | ) |
| x | + | 51 | = | 4 5 | ( | x | + | 78 | ) |
| x | + | 51 | = | 4 5 | x | + | 4 5 | × | 78 |
| x | + | 51 | = | 4 5 | x | + | 312 5 |
| x | − | 4 5 | x | = | 312 5 | − | 51 |
1 5 | x | = | 312 5 | − | 51 |
1 5 | x | = | 57 5 |
| x | = | 57 5 | ÷ | 1 5 |
| = | 57 5 | × | 5 |
| = | 57 | × | 1 |
| x | = | 57 |