| ( | 2 | + | x | ) | ( | 200 | − | x | ÷ | 1 2 | × | 10 | ) | = | 640 |
| Left side of the equation = | 2 | ( | 200 | − | x | ÷ | 1 2 | × | 10 | ) | + | x | ( | 200 | − | x | ÷ | 1 2 | × | 10 | ) |
| = | 2 | × | 200 | − | 2 | x | ÷ | 1 2 | × | 10 | + | x | ( | 200 | − | x | ÷ | 1 2 | × | 10 | ) |
| = | 400 | − | 40 | x | + | x | ( | 200 | − | x | ÷ | 1 2 | × | 10 | ) |
| = | 400 | − | 40 | x | + | x | × | 200 | − | x | x | ÷ | 1 2 | × | 10 |
| = | 400 | − | 40 | x | + | x | × | 200 | − | x | x | × | 20 |
| = | 400 | + | 160 | x | − | x | x | × | 20 |
| 400 | + | 160 | x | − | x | x | × | 20 | = | 640 |