| ( | 200 | − | x | ) | ( | 300 | + | 5 | x | ) | = | 3200 |
| Left side of the equation = | 200 | ( | 300 | + | 5 | x | ) | − | x | ( | 300 | + | 5 | x | ) |
| = | 200 | × | 300 | + | 200 | × | 5 | x | − | x | ( | 300 | + | 5 | x | ) |
| = | 60000 | + | 1000 | x | − | x | ( | 300 | + | 5 | x | ) |
| = | 60000 | + | 1000 | x | − | x | × | 300 | − | x | × | 5 | x |
| = | 60000 | + | 700 | x | − | x | × | 5 | x |
| 60000 | + | 700 | x | − | x | × | 5 | x | = | 3200 |