| ( | 10 | + | m | ) | ( | 500 | − | 20 | m | ) | = | 6000 |
| Left side of the equation = | 10 | ( | 500 | − | 20 | m | ) | + | m | ( | 500 | − | 20 | m | ) |
| = | 10 | × | 500 | − | 10 | × | 20 | m | + | m | ( | 500 | − | 20 | m | ) |
| = | 5000 | − | 200 | m | + | m | ( | 500 | − | 20 | m | ) |
| = | 5000 | − | 200 | m | + | m | × | 500 | − | m | × | 20 | m |
| = | 5000 | + | 300 | m | − | m | × | 20 | m |
| 5000 | + | 300 | m | − | m | × | 20 | m | = | 6000 |