| ( | 100 | + | x | ) | ( | 600 | − | 5 | x | ) | = | 60400 |
| Left side of the equation = | 100 | ( | 600 | − | 5 | x | ) | + | x | ( | 600 | − | 5 | x | ) |
| = | 100 | × | 600 | − | 100 | × | 5 | x | + | x | ( | 600 | − | 5 | x | ) |
| = | 60000 | − | 500 | x | + | x | ( | 600 | − | 5 | x | ) |
| = | 60000 | − | 500 | x | + | x | × | 600 | − | x | × | 5 | x |
| = | 60000 | + | 100 | x | − | x | × | 5 | x |
| 60000 | + | 100 | x | − | x | × | 5 | x | = | 60400 |