| ( | 15 | + | x | ) | ( | 100 | − | 4 | x | ) | = | 1500 |
| Left side of the equation = | 15 | ( | 100 | − | 4 | x | ) | + | x | ( | 100 | − | 4 | x | ) |
| = | 15 | × | 100 | − | 15 | × | 4 | x | + | x | ( | 100 | − | 4 | x | ) |
| = | 1500 | − | 60 | x | + | x | ( | 100 | − | 4 | x | ) |
| = | 1500 | − | 60 | x | + | x | × | 100 | − | x | × | 4 | x |
| = | 1500 | + | 40 | x | − | x | × | 4 | x |
| 1500 | + | 40 | x | − | x | × | 4 | x | = | 1500 |