| ( | 5 | − | 1 10 | a | ) | ( | a | − | 20 | ) | = | 300 |
| Left side of the equation = | 5 | ( | a | − | 20 | ) | − | 1 10 | a | ( | a | − | 20 | ) |
| = | 5 | a | − | 5 | × | 20 | − | 1 10 | a | ( | a | − | 20 | ) |
| = | 5 | a | − | 100 | − | 1 10 | a | ( | a | − | 20 | ) |
| = | 5 | a | − | 100 | − | 1 10 | a | a | + | 1 10 | a | × | 20 |
| = | 5 | a | − | 100 | − | 1 10 | a | a | + | 2 | a |
| = | 7 | a | − | 100 | − | 1 10 | a | a |
| 7 | a | − | 100 | − | 1 10 | a | a | = | 300 |