| ( | 30 | − | x | ) | ( | 100 | + | 5 | x | ) | = | 3000 |
| Left side of the equation = | 30 | ( | 100 | + | 5 | x | ) | − | x | ( | 100 | + | 5 | x | ) |
| = | 30 | × | 100 | + | 30 | × | 5 | x | − | x | ( | 100 | + | 5 | x | ) |
| = | 3000 | + | 150 | x | − | x | ( | 100 | + | 5 | x | ) |
| = | 3000 | + | 150 | x | − | x | × | 100 | − | x | × | 5 | x |
| = | 3000 | + | 50 | x | − | x | × | 5 | x |
| 3000 | + | 50 | x | − | x | × | 5 | x | = | 3000 |