| ( | x | − | 40 | ) | ( | 400 | − | ( | x | − | 50 | ) | × | 10 | ) | = | 6000 |
| Left side of the equation = | x | ( | 400 | − | ( | x | − | 50 | ) | × | 10 | ) | − | 40 | ( | 400 | − | ( | x | − | 50 | ) | × | 10 | ) |
| = | x | × | 400 | − | x | ( | x | − | 50 | ) | × | 10 | − | 40 | ( | 400 | − | ( | x | − | 50 | ) | × | 10 | ) |
| = | 400 | x | − | x | x | × | 10 | + | x | × | 50 | × | 10 | − | 40 | ( | 400 | − | ( | x | − | 50 | ) | × | 10 | ) |
| = | 400 | x | − | x | x | × | 10 | + | x | × | 500 | − | 40 | ( | 400 | − | ( | x | − | 50 | ) | × | 10 | ) |
| = | 900 | x | − | x | x | × | 10 | − | 40 | ( | 400 | − | ( | x | − | 50 | ) | × | 10 | ) |
| = | 900 | x | − | x | x | × | 10 | − | 40 | × | 400 | + | 40 | ( | x | − | 50 | ) | × | 10 |
| = | 900 | x | − | x | x | × | 10 | − | 16000 | + | 400 | ( | x | − | 50 | ) |
| = | 900 | x | − | x | x | × | 10 | − | 16000 | + | 400 | x | − | 400 | × | 50 |
| = | 900 | x | − | x | x | × | 10 | − | 16000 | + | 400 | x | − | 20000 |
| = | 1300 | x | − | x | x | × | 10 | − | 36000 |
| 1300 | x | − | x | x | × | 10 | − | 36000 | = | 6000 |