| ( | x | − | 40 | ) | ( | 100 | − | x | − | 60 | ) | = | 2250 |
| Left side of the equation = | x | ( | 100 | − | x | − | 60 | ) | − | 40 | ( | 100 | − | x | − | 60 | ) |
| = | x | × | 100 | − | x | x | − | x | × | 60 | − | 40 | ( | 100 | − | x | − | 60 | ) |
| = | 40 | x | − | x | x | − | 40 | ( | 100 | − | x | − | 60 | ) |
| = | 40 | x | − | x | x | − | 40 | × | 100 | + | 40 | x | + | 40 | × | 60 |
| = | 40 | x | − | x | x | − | 4000 | + | 40 | x | + | 2400 |
| = | 80 | x | − | x | x | − | 1600 |
| 80 | x | − | x | x | − | 1600 | = | 2250 |