| 80 | × | 200 | + | ( | 80 | − | x | ) | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) | − | 40000 | = | 9000 |
| Left side of the equation = | 16000 | + | ( | 80 | − | x | ) | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) | − | 40000 |
| = | - | 24000 | + | ( | 80 | − | x | ) | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) |
| - | 24000 | + | ( | 80 | − | x | ) | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) | = | 9000 |
| Left side of the equation = | - | 24000 | + | 80 | ( | 200 | + | 10 | x | ) | − | x | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) |
| = | - | 24000 | + | 80 | × | 200 | + | 80 | × | 10 | x | − | x | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) |
| = | - | 24000 | + | 16000 | + | 800 | x | − | x | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) |
| = | - | 8000 | + | 800 | x | − | x | ( | 200 | + | 10 | x | ) | + | 40 | ( | 400 | + | 10 | x | ) |
| = | - | 8000 | + | 800 | x | − | x | × | 200 | − | x | × | 10 | x | + | 40 | ( | 400 | + | 10 | x | ) |
| = | - | 8000 | + | 600 | x | − | x | × | 10 | x | + | 40 | ( | 400 | + | 10 | x | ) |
| = | - | 8000 | + | 600 | x | − | x | × | 10 | x | + | 40 | × | 400 | + | 40 | × | 10 | x |
| = | - | 8000 | + | 600 | x | − | x | × | 10 | x | + | 16000 | + | 400 | x |
| = | 8000 | + | 1000 | x | − | x | × | 10 | x |
| 8000 | + | 1000 | x | − | x | × | 10 | x | = | 9000 |