| ( | x | − | 30 | ) | ( | 140 | − | 2 | x | ) | = | 600 |
| Left side of the equation = | x | ( | 140 | − | 2 | x | ) | − | 30 | ( | 140 | − | 2 | x | ) |
| = | x | × | 140 | − | x | × | 2 | x | − | 30 | ( | 140 | − | 2 | x | ) |
| = | 140 | x | − | x | × | 2 | x | − | 30 | × | 140 | + | 30 | × | 2 | x |
| = | 140 | x | − | x | × | 2 | x | − | 4200 | + | 60 | x |
| = | 200 | x | − | x | × | 2 | x | − | 4200 |
| 200 | x | − | x | × | 2 | x | − | 4200 | = | 600 |