| ( | x | + | 40 | − | 30 | ) | ( | 500 | − | 10 | x | ) | = | 8000 |
| Left side of the equation = | x | ( | 500 | − | 10 | x | ) | + | 40 | ( | 500 | − | 10 | x | ) | − | 30 | ( | 500 | − | 10 | x | ) |
| = | x | × | 500 | − | x | × | 10 | x | + | 40 | ( | 500 | − | 10 | x | ) | − | 30 | ( | 500 | − | 10 | x | ) |
| = | 500 | x | − | x | × | 10 | x | + | 40 | × | 500 | − | 40 | × | 10 | x | − | 30 | ( | 500 | − | 10 | x | ) |
| = | 500 | x | − | x | × | 10 | x | + | 20000 | − | 400 | x | − | 30 | ( | 500 | − | 10 | x | ) |
| = | 100 | x | − | x | × | 10 | x | + | 20000 | − | 30 | ( | 500 | − | 10 | x | ) |
| = | 100 | x | − | x | × | 10 | x | + | 20000 | − | 30 | × | 500 | + | 30 | × | 10 | x |
| = | 100 | x | − | x | × | 10 | x | + | 20000 | − | 15000 | + | 300 | x |
| = | 400 | x | − | x | × | 10 | x | + | 5000 |
| 400 | x | − | x | × | 10 | x | + | 5000 | = | 8000 |