| ( | 400 | − | 100 | a | ) | ( | 8 | + | 2 | a | ) | + | ( | 500 | − | 100 | ) | ( | 8 | + | a | ) | = | 6400 |
| Left side of the equation = | 400 | ( | 8 | + | 2 | a | ) | − | 100 | a | ( | 8 | + | 2 | a | ) | + | ( | 500 | − | 100 | ) | ( | 8 | + | a | ) |
| = | 400 | × | 8 | + | 400 | × | 2 | a | − | 100 | a | ( | 8 | + | 2 | a | ) | + | ( | 500 | − | 100 | ) | ( | 8 | + | a | ) |
| = | 3200 | + | 800 | a | − | 100 | a | ( | 8 | + | 2 | a | ) | + | ( | 500 | − | 100 | ) | ( | 8 | + | a | ) |
| = | 3200 | + | 800 | a | − | 100 | a | × | 8 | − | 100 | a | × | 2 | a | + | ( | 500 | − | 100 | ) | ( | 8 | + | a | ) |
| = | 3200 | + | 800 | a | − | 800 | a | − | 200 | a | a | + | ( | 500 | − | 100 | ) | ( | 8 | + | a | ) |
| = | 3200 | + | 0 | a | − | 200 | a | a | + | ( | 500 | − | 100 | ) | ( | 8 | + | a | ) |
| = | 3200 | + | 0 | a | − | 200 | a | a | + | 500 | ( | 8 | + | a | ) | − | 100 | ( | 8 | + | a | ) |
| = | 3200 | + | 0 | a | − | 200 | a | a | + | 500 | × | 8 | + | 500 | a | − | 100 | ( | 8 | + | a | ) |
| = | 3200 | + | 0 | a | − | 200 | a | a | + | 4000 | + | 500 | a | − | 100 | ( | 8 | + | a | ) |
| = | 7200 | + | 500 | a | − | 200 | a | a | − | 100 | ( | 8 | + | a | ) |
| = | 7200 | + | 500 | a | − | 200 | a | a | − | 100 | × | 8 | − | 100 | a |
| = | 7200 | + | 500 | a | − | 200 | a | a | − | 800 | − | 100 | a |
| = | 6400 | + | 400 | a | − | 200 | a | a |
| 6400 | + | 400 | a | − | 200 | a | a | = | 6400 |