| ( | 180 | − | x | ) | ( | 50 | + | 1 2 | x | ) | = | 9600 |
| Left side of the equation = | 180 | ( | 50 | + | 1 2 | x | ) | − | x | ( | 50 | + | 1 2 | x | ) |
| = | 180 | × | 50 | + | 180 | × | 1 2 | x | − | x | ( | 50 | + | 1 2 | x | ) |
| = | 9000 | + | 90 | x | − | x | ( | 50 | + | 1 2 | x | ) |
| = | 9000 | + | 90 | x | − | x | × | 50 | − | x | × | 1 2 | x |
| = | 9000 | + | 40 | x | − | x | × | 1 2 | x |
| 9000 | + | 40 | x | − | x | × | 1 2 | x | = | 9600 |