| ( | 6 | + | x | ) | ( | 120 | − | 10 | x | ) | = | 770 |
| Left side of the equation = | 6 | ( | 120 | − | 10 | x | ) | + | x | ( | 120 | − | 10 | x | ) |
| = | 6 | × | 120 | − | 6 | × | 10 | x | + | x | ( | 120 | − | 10 | x | ) |
| = | 720 | − | 60 | x | + | x | ( | 120 | − | 10 | x | ) |
| = | 720 | − | 60 | x | + | x | × | 120 | − | x | × | 10 | x |
| = | 720 | + | 60 | x | − | x | × | 10 | x |
| 720 | + | 60 | x | − | x | × | 10 | x | = | 770 |