| ( | x | − | 3 | ) | ( | 500 | − | 100 | ( | x | − | 4 | ) | ) | = | 800 |
| Left side of the equation = | x | ( | 500 | − | 100 | ( | x | − | 4 | ) | ) | − | 3 | ( | 500 | − | 100 | ( | x | − | 4 | ) | ) |
| = | x | × | 500 | − | x | × | 100 | ( | x | − | 4 | ) | − | 3 | ( | 500 | − | 100 | ( | x | − | 4 | ) | ) |
| = | 500 | x | − | x | × | 100 | x | + | x | × | 100 | × | 4 | − | 3 | ( | 500 | − | 100 | ( | x | − | 4 | ) | ) |
| = | 500 | x | − | x | × | 100 | x | + | x | × | 400 | − | 3 | ( | 500 | − | 100 | ( | x | − | 4 | ) | ) |
| = | 900 | x | − | x | × | 100 | x | − | 3 | ( | 500 | − | 100 | ( | x | − | 4 | ) | ) |
| = | 900 | x | − | x | × | 100 | x | − | 3 | × | 500 | + | 3 | × | 100 | ( | x | − | 4 | ) |
| = | 900 | x | − | x | × | 100 | x | − | 1500 | + | 300 | ( | x | − | 4 | ) |
| = | 900 | x | − | x | × | 100 | x | − | 1500 | + | 300 | x | − | 300 | × | 4 |
| = | 900 | x | − | x | × | 100 | x | − | 1500 | + | 300 | x | − | 1200 |
| = | 1200 | x | − | x | × | 100 | x | − | 2700 |
| 1200 | x | − | x | × | 100 | x | − | 2700 | = | 800 |