| ( | 50 | + | m | − | 40 | ) | ( | 500 | − | 20 | m | ) | = | 6000 |
| Left side of the equation = | 50 | ( | 500 | − | 20 | m | ) | + | m | ( | 500 | − | 20 | m | ) | − | 40 | ( | 500 | − | 20 | m | ) |
| = | 50 | × | 500 | − | 50 | × | 20 | m | + | m | ( | 500 | − | 20 | m | ) | − | 40 | ( | 500 | − | 20 | m | ) |
| = | 25000 | − | 1000 | m | + | m | ( | 500 | − | 20 | m | ) | − | 40 | ( | 500 | − | 20 | m | ) |
| = | 25000 | − | 1000 | m | + | m | × | 500 | − | m | × | 20 | m | − | 40 | ( | 500 | − | 20 | m | ) |
| = | 25000 | − | 500 | m | − | m | × | 20 | m | − | 40 | ( | 500 | − | 20 | m | ) |
| = | 25000 | − | 500 | m | − | m | × | 20 | m | − | 40 | × | 500 | + | 40 | × | 20 | m |
| = | 25000 | − | 500 | m | − | m | × | 20 | m | − | 20000 | + | 800 | m |
| = | 5000 | + | 300 | m | − | m | × | 20 | m |
| 5000 | + | 300 | m | − | m | × | 20 | m | = | 6000 |