| 6 | x | + | 10 | ( | 50 | − | x | ) | + | 2 | = | 500 | − | 78 |
| Left side of the equation = | 6 | x | + | 10 | × | 50 | − | 10 | x | + | 2 |
| = | 6 | x | + | 500 | − | 10 | x | + | 2 |
| = | - | 4 | x | + | 502 |
| - | 4 | x | + | 502 | = | 500 | − | 78 |
| Right side of the equation = | 422 |
| - | 4 | x | + | 502 | = | 422 |
| - | 4 | x | = | 422 | − | 502 |
| - | 4 | x | = | - | 80 |
| 80 | = | 4 | x |
| 4 | x | = | 80 |
| x | = | 80 | ÷ | 4 |
| = | 80 | × | 1 4 |
| = | 20 | × | 1 |
| x | = | 20 |