| ( | 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 | ) | ÷ | 50 | − | 1000 | ( | 4 | + | ( | 1800 | − | x | ) | ÷ | 50 | ) |
| = | 4 | x | + | x | × | 1800 | × | 1 50 | − | x | x | × | 1 50 | − | 1000 | ( | 4 | + | ( | 1800 | − | x | ) | ÷ | 50 | ) |
| = | 4 | x | + | x | × | 36 | − | x | x | × | 1 50 | − | 1000 | ( | 4 | + | ( | 1800 | − | x | ) | ÷ | 50 | ) |
| = | 40 | x | − | x | x | × | 1 50 | − | 1000 | ( | 4 | + | ( | 1800 | − | x | ) | ÷ | 50 | ) |
| = | 40 | x | − | x | x | × | 1 50 | − | 1000 | × | 4 | − | 1000 | ( | 1800 | − | x | ) | ÷ | 50 |
| = | 40 | x | − | x | x | × | 1 50 | − | 4000 | − | 20 | ( | 1800 | − | x | ) |
| = | 40 | x | − | x | x | × | 1 50 | − | 4000 | − | 20 | × | 1800 | + | 20 | x |
| = | 40 | x | − | x | x | × | 1 50 | − | 4000 | − | 36000 | + | 20 | x |
| = | 60 | x | − | x | x | × | 1 50 | − | 40000 |
| 60 | x | − | x | x | × | 1 50 | − | 40000 | = | 4200 |