| ( | x | − | 80 | ) | ( | 500 | − | 10 | x | + | 1000 | ) | = | 12000 |
| Left side of the equation = | x | ( | 500 | − | 10 | x | + | 1000 | ) | − | 80 | ( | 500 | − | 10 | x | + | 1000 | ) |
| = | x | × | 500 | − | x | × | 10 | x | + | x | × | 1000 | − | 80 | ( | 500 | − | 10 | x | + | 1000 | ) |
| = | 1500 | x | − | x | × | 10 | x | − | 80 | ( | 500 | − | 10 | x | + | 1000 | ) |
| = | 1500 | x | − | x | × | 10 | x | − | 80 | × | 500 | + | 80 | × | 10 | x | − | 80 | × | 1000 |
| = | 1500 | x | − | x | × | 10 | x | − | 40000 | + | 800 | x | − | 80000 |
| = | 2300 | x | − | x | × | 10 | x | − | 120000 |
| 2300 | x | − | x | × | 10 | x | − | 120000 | = | 12000 |