| ( | 30 | + | x | ) | ( | 100 | − | 2 | x | ) | = | 3150 |
| Left side of the equation = | 30 | ( | 100 | − | 2 | x | ) | + | x | ( | 100 | − | 2 | x | ) |
| = | 30 | × | 100 | − | 30 | × | 2 | x | + | x | ( | 100 | − | 2 | x | ) |
| = | 3000 | − | 60 | x | + | x | ( | 100 | − | 2 | x | ) |
| = | 3000 | − | 60 | x | + | x | × | 100 | − | x | × | 2 | x |
| = | 3000 | + | 40 | x | − | x | × | 2 | x |
| 3000 | + | 40 | x | − | x | × | 2 | x | = | 3150 |