| ( | 40 | − | x | ) | ( | 50 | − | 4 | x | ) | = | 2250 |
| Left side of the equation = | 40 | ( | 50 | − | 4 | x | ) | − | x | ( | 50 | − | 4 | x | ) |
| = | 40 | × | 50 | − | 40 | × | 4 | x | − | x | ( | 50 | − | 4 | x | ) |
| = | 2000 | − | 160 | x | − | x | ( | 50 | − | 4 | x | ) |
| = | 2000 | − | 160 | x | − | x | × | 50 | + | x | × | 4 | x |
| = | 2000 | − | 210 | x | + | x | × | 4 | x |
| 2000 | − | 210 | x | + | x | × | 4 | x | = | 2250 |