| ( | 80 | − | x | ) | ( | 50 | x | + | 1000 | ) | = | 12000 |
| Left side of the equation = | 80 | ( | 50 | x | + | 1000 | ) | − | x | ( | 50 | x | + | 1000 | ) |
| = | 80 | × | 50 | x | + | 80 | × | 1000 | − | x | ( | 50 | x | + | 1000 | ) |
| = | 4000 | x | + | 80000 | − | x | ( | 50 | x | + | 1000 | ) |
| = | 4000 | x | + | 80000 | − | x | × | 50 | x | − | x | × | 1000 |
| = | 3000 | x | + | 80000 | − | x | × | 50 | x |
| 3000 | x | + | 80000 | − | x | × | 50 | x | = | 12000 |