| ( | x | + | 15 | ) | ( | 300 | − | 10 | x | ) | = | 5000 |
| Left side of the equation = | x | ( | 300 | − | 10 | x | ) | + | 15 | ( | 300 | − | 10 | x | ) |
| = | x | × | 300 | − | x | × | 10 | x | + | 15 | ( | 300 | − | 10 | x | ) |
| = | 300 | x | − | x | × | 10 | x | + | 15 | × | 300 | − | 15 | × | 10 | x |
| = | 300 | x | − | x | × | 10 | x | + | 4500 | − | 150 | x |
| = | 150 | x | − | x | × | 10 | x | + | 4500 |
| 150 | x | − | x | × | 10 | x | + | 4500 | = | 5000 |