| ( | x | − | 50 | ) | ( | 80 | − | 2 | ( | x | − | 60 | ) | ) | = | 1200 |
| Left side of the equation = | x | ( | 80 | − | 2 | ( | x | − | 60 | ) | ) | − | 50 | ( | 80 | − | 2 | ( | x | − | 60 | ) | ) |
| = | x | × | 80 | − | x | × | 2 | ( | x | − | 60 | ) | − | 50 | ( | 80 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 80 | x | − | x | × | 2 | x | + | x | × | 2 | × | 60 | − | 50 | ( | 80 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 80 | x | − | x | × | 2 | x | + | x | × | 120 | − | 50 | ( | 80 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 200 | x | − | x | × | 2 | x | − | 50 | ( | 80 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 200 | x | − | x | × | 2 | x | − | 50 | × | 80 | + | 50 | × | 2 | ( | x | − | 60 | ) |
| = | 200 | x | − | x | × | 2 | x | − | 4000 | + | 100 | ( | x | − | 60 | ) |
| = | 200 | x | − | x | × | 2 | x | − | 4000 | + | 100 | x | − | 100 | × | 60 |
| = | 200 | x | − | x | × | 2 | x | − | 4000 | + | 100 | x | − | 6000 |
| = | 300 | x | − | x | × | 2 | x | − | 10000 |
| 300 | x | − | x | × | 2 | x | − | 10000 | = | 1200 |