| 800 | + | ( | 4 | − | x | ) | ( | 200 | + | 50 | x | ) | + | ( | 100 | x | − | 400 | ) | = | 1250 |
| Left side of the equation = | 800 | + | 4 | ( | 200 | + | 50 | x | ) | − | x | ( | 200 | + | 50 | x | ) | + | ( | 100 | x | − | 400 | ) |
| = | 800 | + | 4 | × | 200 | + | 4 | × | 50 | x | − | x | ( | 200 | + | 50 | x | ) | + | ( | 100 | x | − | 400 | ) |
| = | 800 | + | 800 | + | 200 | x | − | x | ( | 200 | + | 50 | x | ) | + | ( | 100 | x | − | 400 | ) |
| = | 1600 | + | 200 | x | − | x | ( | 200 | + | 50 | x | ) | + | ( | 100 | x | − | 400 | ) |
| = | 1600 | + | 200 | x | − | x | × | 200 | − | x | × | 50 | x | + | ( | 100 | x | − | 400 | ) |
| = | 1600 | + | 0 | x | − | x | × | 50 | x | + | ( | 100 | x | − | 400 | ) |
| = | 1600 | + | 0 | x | − | x | × | 50 | x | + | 100 | x | − | 400 |
| = | 1200 | + | 100 | x | − | x | × | 50 | x |
| 1200 | + | 100 | x | − | x | × | 50 | x | = | 1250 |