| 80 | × | 200 | + | ( | 80 | − | x | ) | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) | − | 50 | × | 800 | = | 9000 |
| Left side of the equation = | 16000 | + | ( | 80 | − | x | ) | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) | − | 40000 |
| = | - | 24000 | + | ( | 80 | − | x | ) | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) |
| - | 24000 | + | ( | 80 | − | x | ) | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) | = | 9000 |
| Left side of the equation = | - | 24000 | + | 80 | ( | 200 | + | x | ) | − | x | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) |
| = | - | 24000 | + | 80 | × | 200 | + | 80 | x | − | x | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) |
| = | - | 24000 | + | 16000 | + | 80 | x | − | x | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) |
| = | - | 8000 | + | 80 | x | − | x | ( | 200 | + | x | ) | + | 40 | ( | 400 | − | 2 | x | ) |
| = | - | 8000 | + | 80 | x | − | x | × | 200 | − | x | x | + | 40 | ( | 400 | − | 2 | x | ) |
| = | - | 8000 | − | 120 | x | − | x | x | + | 40 | ( | 400 | − | 2 | x | ) |
| = | - | 8000 | − | 120 | x | − | x | x | + | 40 | × | 400 | − | 40 | × | 2 | x |
| = | - | 8000 | − | 120 | x | − | x | x | + | 16000 | − | 80 | x |
| = | 8000 | − | 200 | x | − | x | x |
| 8000 | − | 200 | x | − | x | x | = | 9000 |