| ( | 420 | − | 2 | x | ) | ( | x | − | 150 | ) | = | 1750 |
| Left side of the equation = | 420 | ( | x | − | 150 | ) | − | 2 | x | ( | x | − | 150 | ) |
| = | 420 | x | − | 420 | × | 150 | − | 2 | x | ( | x | − | 150 | ) |
| = | 420 | x | − | 63000 | − | 2 | x | ( | x | − | 150 | ) |
| = | 420 | x | − | 63000 | − | 2 | x | x | + | 2 | x | × | 150 |
| = | 420 | x | − | 63000 | − | 2 | x | x | + | 300 | x |
| = | 720 | x | − | 63000 | − | 2 | x | x |
| 720 | x | − | 63000 | − | 2 | x | x | = | 1750 |