| ( | 800 | − | x | ) | ( | 4 | + | x | ÷ | 50 | ) | = | 4200 |
| Left side of the equation = | 800 | ( | 4 | + | x | ÷ | 50 | ) | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 800 | × | 4 | + | 800 | x | ÷ | 50 | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 3200 | + | 16 | x | − | x | ( | 4 | + | x | ÷ | 50 | ) |
| = | 3200 | + | 16 | x | − | x | × | 4 | − | x | x | ÷ | 50 |
| = | 3200 | + | 12 | x | − | x | x | × | 1 50 |
| 3200 | + | 12 | x | − | x | x | × | 1 50 | = | 4200 |