| ( | 10 | − | x | ) | ( | 800 | + | 300 | x | ) | = | 12000 |
| Left side of the equation = | 10 | ( | 800 | + | 300 | x | ) | − | x | ( | 800 | + | 300 | x | ) |
| = | 10 | × | 800 | + | 10 | × | 300 | x | − | x | ( | 800 | + | 300 | x | ) |
| = | 8000 | + | 3000 | x | − | x | ( | 800 | + | 300 | x | ) |
| = | 8000 | + | 3000 | x | − | x | × | 800 | − | x | × | 300 | x |
| = | 8000 | + | 2200 | x | − | x | × | 300 | x |
| 8000 | + | 2200 | x | − | x | × | 300 | x | = | 12000 |
| x1= | 10 3 |
| x2=4 |