| ( | 20 | − | x | ) | ( | 100 | + | 5 | x | ) | + | 2000 | − | 1800 | = | 2020 |
| Left side of the equation = | ( | 20 | − | x | ) | ( | 100 | + | 5 | x | ) | + | 200 |
| ( | 20 | − | x | ) | ( | 100 | + | 5 | x | ) | + | 200 | = | 2020 |
| Left side of the equation = | 20 | ( | 100 | + | 5 | x | ) | − | x | ( | 100 | + | 5 | x | ) | + | 200 |
| = | 20 | × | 100 | + | 20 | × | 5 | x | − | x | ( | 100 | + | 5 | x | ) | + | 200 |
| = | 2000 | + | 100 | x | − | x | ( | 100 | + | 5 | x | ) | + | 200 |
| = | 2200 | + | 100 | x | − | x | ( | 100 | + | 5 | x | ) |
| = | 2200 | + | 100 | x | − | x | × | 100 | − | x | × | 5 | x |
| = | 2200 | + | 0 | x | − | x | × | 5 | x |
| 2200 | + | 0 | x | − | x | × | 5 | x | = | 2020 |