| 500 | ( | a | − | 35 | ) | + | 20 | a | ( | a | − | 35 | ) | = | 8400 |
| Left side of the equation = | 500 | a | − | 500 | × | 35 | + | 20 | a | ( | a | − | 35 | ) |
| = | 500 | a | − | 17500 | + | 20 | a | ( | a | − | 35 | ) |
| = | 500 | a | − | 17500 | + | 20 | a | a | − | 20 | a | × | 35 |
| = | 500 | a | − | 17500 | + | 20 | a | a | − | 700 | a |
| = | - | 200 | a | − | 17500 | + | 20 | a | a |
| - | 200 | a | − | 17500 | + | 20 | a | a | = | 8400 |