| ( | x | + | 10 | ) | ( | 300 | − | 10 | x | ) | = | 3360 |
| Left side of the equation = | x | ( | 300 | − | 10 | x | ) | + | 10 | ( | 300 | − | 10 | x | ) |
| = | x | × | 300 | − | x | × | 10 | x | + | 10 | ( | 300 | − | 10 | x | ) |
| = | 300 | x | − | x | × | 10 | x | + | 10 | × | 300 | − | 10 | × | 10 | x |
| = | 300 | x | − | x | × | 10 | x | + | 3000 | − | 100 | x |
| = | 200 | x | − | x | × | 10 | x | + | 3000 |
| 200 | x | − | x | × | 10 | x | + | 3000 | = | 3360 |