| ( | 6 | − | x | ) | ( | 100 | + | 200 | x | ) | = | 300 |
| Left side of the equation = | 6 | ( | 100 | + | 200 | x | ) | − | x | ( | 100 | + | 200 | x | ) |
| = | 6 | × | 100 | + | 6 | × | 200 | x | − | x | ( | 100 | + | 200 | x | ) |
| = | 600 | + | 1200 | x | − | x | ( | 100 | + | 200 | x | ) |
| = | 600 | + | 1200 | x | − | x | × | 100 | − | x | × | 200 | x |
| = | 600 | + | 1100 | x | − | x | × | 200 | x |
| 600 | + | 1100 | x | − | x | × | 200 | x | = | 300 |