| ( | 20 | − | x | ) | + | 10 | ( | x | ÷ | 5 | ) | ( | 20 | − | x | ) | = | 400 |
| Left side of the equation = | 20 | − | x | + | 10 | ( | x | ÷ | 5 | ) | ( | 20 | − | x | ) |
| = | 20 | − | x | + | 10 | x | ÷ | 5 | × | ( | 20 | − | x | ) |
| = | 20 | − | x | + | 2 | x | ( | 20 | − | x | ) |
| = | 20 | − | x | + | 2 | x | × | 20 | − | 2 | x | x |
| = | 20 | − | x | + | 40 | x | − | 2 | x | x |
| = | 20 | + | 39 | x | − | 2 | x | x |
| 20 | + | 39 | x | − | 2 | x | x | = | 400 |