| ( | a | − | 40 | ) | ( | 200 | + | 20 | ( | 100 | − | a | ) | ) | − | 2000 | = | 22500 |
| Left side of the equation = | a | ( | 200 | + | 20 | ( | 100 | − | a | ) | ) | − | 40 | ( | 200 | + | 20 | ( | 100 | − | a | ) | ) | − | 2000 |
| = | a | × | 200 | + | a | × | 20 | ( | 100 | − | a | ) | − | 40 | ( | 200 | + | 20 | ( | 100 | − | a | ) | ) | − | 2000 |
| = | 200 | a | + | a | × | 20 | × | 100 | − | a | × | 20 | a | − | 40 | ( | 200 | + | 20 | ( | 100 | − | a | ) | ) | − | 2000 |
| = | 200 | a | + | a | × | 2000 | − | a | × | 20 | a | − | 40 | ( | 200 | + | 20 | ( | 100 | − | a | ) | ) | − | 2000 |
| = | 2200 | a | − | a | × | 20 | a | − | 40 | ( | 200 | + | 20 | ( | 100 | − | a | ) | ) | − | 2000 |
| = | 2200 | a | − | a | × | 20 | a | − | 40 | × | 200 | − | 40 | × | 20 | ( | 100 | − | a | ) | − | 2000 |
| = | 2200 | a | − | a | × | 20 | a | − | 8000 | − | 800 | ( | 100 | − | a | ) | − | 2000 |
| = | 2200 | a | − | a | × | 20 | a | − | 10000 | − | 800 | ( | 100 | − | a | ) |
| = | 2200 | a | − | a | × | 20 | a | − | 10000 | − | 800 | × | 100 | + | 800 | a |
| = | 2200 | a | − | a | × | 20 | a | − | 10000 | − | 80000 | + | 800 | a |
| = | 3000 | a | − | a | × | 20 | a | − | 90000 |
| 3000 | a | − | a | × | 20 | a | − | 90000 | = | 22500 |