| 8000 | = | ( | 400 | − | 2 | x | ) | ( | x | − | 60 | ) |
| Right side of the equation = | 400 | ( | x | − | 60 | ) | − | 2 | x | ( | x | − | 60 | ) |
| = | 400 | x | − | 400 | × | 60 | − | 2 | x | ( | x | − | 60 | ) |
| = | 400 | x | − | 24000 | − | 2 | x | ( | x | − | 60 | ) |
| = | 400 | x | − | 24000 | − | 2 | x | x | + | 2 | x | × | 60 |
| = | 400 | x | − | 24000 | − | 2 | x | x | + | 120 | x |
| = | 520 | x | − | 24000 | − | 2 | x | x |
| 8000 | = | 520 | x | − | 24000 | − | 2 | x | x |