| ( | x | − | 1000 | ) | ( | 4 | + | 1800 | − | x | ÷ | 50 | ) | = | 4200 |
| Left side of the equation = | x | ( | 4 | + | 1800 | − | x | ÷ | 50 | ) | − | 1000 | ( | 4 | + | 1800 | − | x | ÷ | 50 | ) |
| = | x | × | 4 | + | x | × | 1800 | − | x | x | ÷ | 50 | − | 1000 | ( | 4 | + | 1800 | − | x | ÷ | 50 | ) |
| = | 1804 | x | − | x | x | × | 1 50 | − | 1000 | ( | 4 | + | 1800 | − | x | ÷ | 50 | ) |
| = | 1804 | x | − | x | x | × | 1 50 | − | 1000 | × | 4 | − | 1000 | × | 1800 | + | 1000 | x | ÷ | 50 |
| = | 1804 | x | − | x | x | × | 1 50 | − | 4000 | − | 1800000 | + | 20 | x |
| = | 1824 | x | − | x | x | × | 1 50 | − | 1804000 |
| 1824 | x | − | x | x | × | 1 50 | − | 1804000 | = | 4200 |