| ( | 120 | − | 1 2 | x | ) | ( | 60 | + | x | ) | = | 8800 |
| Left side of the equation = | 120 | ( | 60 | + | x | ) | − | 1 2 | x | ( | 60 | + | x | ) |
| = | 120 | × | 60 | + | 120 | x | − | 1 2 | x | ( | 60 | + | x | ) |
| = | 7200 | + | 120 | x | − | 1 2 | x | ( | 60 | + | x | ) |
| = | 7200 | + | 120 | x | − | 1 2 | x | × | 60 | − | 1 2 | x | x |
| = | 7200 | + | 120 | x | − | 30 | x | − | 1 2 | x | x |
| = | 7200 | + | 90 | x | − | 1 2 | x | x |
| 7200 | + | 90 | x | − | 1 2 | x | x | = | 8800 |