| ( | 40 | − | X | ) | ( | 300 | + | 20 | X | ) | = | 6080 |
| Left side of the equation = | 40 | ( | 300 | + | 20 | X | ) | − | X | ( | 300 | + | 20 | X | ) |
| = | 40 | × | 300 | + | 40 | × | 20 | X | − | X | ( | 300 | + | 20 | X | ) |
| = | 12000 | + | 800 | X | − | X | ( | 300 | + | 20 | X | ) |
| = | 12000 | + | 800 | X | − | X | × | 300 | − | X | × | 20 | X |
| = | 12000 | + | 500 | X | − | X | × | 20 | X |
| 12000 | + | 500 | X | − | X | × | 20 | X | = | 6080 |