| ( | x | − | 4 | ) | ( | - | 50 | x | + | 800 | ) | = | 1350 |
| Left side of the equation = | x | ( | - | 50 | x | + | 800 | ) | − | 4 | ( | - | 50 | x | + | 800 | ) |
| = | - | x | × | 50 | x | + | x | × | 800 | − | 4 | ( | - | 50 | x | + | 800 | ) |
| = | - | x | × | 50 | x | + | 800 | x | + | 4 | × | 50 | x | − | 4 | × | 800 |
| = | - | x | × | 50 | x | + | 800 | x | + | 200 | x | − | 3200 |
| = | - | x | × | 50 | x | + | 1000 | x | − | 3200 |
| - | x | × | 50 | x | + | 1000 | x | − | 3200 | = | 1350 |