| ( | 3 10 | + | x | ) | ( | 500 | − | 40 | x | ) | = | 180 |
| Left side of the equation = | 3 10 | ( | 500 | − | 40 | x | ) | + | x | ( | 500 | − | 40 | x | ) |
| = | 3 10 | × | 500 | − | 3 10 | × | 40 | x | + | x | ( | 500 | − | 40 | x | ) |
| = | 150 | − | 12 | x | + | x | ( | 500 | − | 40 | x | ) |
| = | 150 | − | 12 | x | + | x | × | 500 | − | x | × | 40 | x |
| = | 150 | + | 488 | x | − | x | × | 40 | x |
| 150 | + | 488 | x | − | x | × | 40 | x | = | 180 |