| 60 | × | 120 | + | ( | x | − | 60 | ) | ( | 120 | − | 1 2 | x | + | 30 | ) | = | 8800 |
| Left side of the equation = | 7200 | + | ( | x | − | 60 | ) | ( | 120 | − | 1 2 | x | + | 30 | ) |
| 7200 | + | ( | x | − | 60 | ) | ( | 120 | − | 1 2 | x | + | 30 | ) | = | 8800 |
| Left side of the equation = | 7200 | + | x | ( | 120 | − | 1 2 | x | + | 30 | ) | − | 60 | ( | 120 | − | 1 2 | x | + | 30 | ) |
| = | 7200 | + | x | × | 120 | − | x | × | 1 2 | x | + | x | × | 30 | − | 60 | ( | 120 | − | 1 2 | x | + | 30 | ) |
| = | 7200 | + | 150 | x | − | x | × | 1 2 | x | − | 60 | ( | 120 | − | 1 2 | x | + | 30 | ) |
| = | 7200 | + | 150 | x | − | x | × | 1 2 | x | − | 60 | × | 120 | + | 60 | × | 1 2 | x | − | 60 |
| = | 7200 | + | 150 | x | − | x | × | 1 2 | x | − | 7200 | + | 30 | x | − | 1800 |
| = | - | 1800 | + | 180 | x | − | x | × | 1 2 | x |
| - | 1800 | + | 180 | x | − | x | × | 1 2 | x | = | 8800 |