| ( | 200 | + | 50 | x | ) | ( | 4 | − | x | ) | − | ( | 400 | − | 200 | − | 50 | x | ) | = | 1250 | − | 800 |
| Left side of the equation = | 200 | ( | 4 | − | x | ) | + | 50 | x | ( | 4 | − | x | ) | − | ( | 400 | − | 200 | − | 50 | x | ) |
| = | 200 | × | 4 | − | 200 | x | + | 50 | x | ( | 4 | − | x | ) | − | ( | 400 | − | 200 | − | 50 | x | ) |
| = | 800 | − | 200 | x | + | 50 | x | ( | 4 | − | x | ) | − | ( | 400 | − | 200 | − | 50 | x | ) |
| = | 800 | − | 200 | x | + | 50 | x | × | 4 | − | 50 | x | x | − | ( | 400 | − | 200 | − | 50 | x | ) |
| = | 800 | − | 200 | x | + | 200 | x | − | 50 | x | x | − | ( | 400 | − | 200 | − | 50 | x | ) |
| = | 800 | − | 0 | x | − | 50 | x | x | − | ( | 400 | − | 200 | − | 50 | x | ) |
| = | 800 | − | 0 | x | − | 50 | x | x | − | 400 | + | 200 | + | 50 | x |
| = | 600 | + | 50 | x | − | 50 | x | x |
| 600 | + | 50 | x | − | 50 | x | x | = | 1250 | − | 800 |
| Right side of the equation = | 450 |
| 600 | + | 50 | x | − | 50 | x | x | = | 450 |