| ( | 50 | − | x | ) | ( | 160 | + | 10 | x | ) | = | 10800 |
| Left side of the equation = | 50 | ( | 160 | + | 10 | x | ) | − | x | ( | 160 | + | 10 | x | ) |
| = | 50 | × | 160 | + | 50 | × | 10 | x | − | x | ( | 160 | + | 10 | x | ) |
| = | 8000 | + | 500 | x | − | x | ( | 160 | + | 10 | x | ) |
| = | 8000 | + | 500 | x | − | x | × | 160 | − | x | × | 10 | x |
| = | 8000 | + | 340 | x | − | x | × | 10 | x |
| 8000 | + | 340 | x | − | x | × | 10 | x | = | 10800 |