| ( | 60 | − | x | ) | ( | 20 | + | 2 | x | ) | = | 2400 |
| Left side of the equation = | 60 | ( | 20 | + | 2 | x | ) | − | x | ( | 20 | + | 2 | x | ) |
| = | 60 | × | 20 | + | 60 | × | 2 | x | − | x | ( | 20 | + | 2 | x | ) |
| = | 1200 | + | 120 | x | − | x | ( | 20 | + | 2 | x | ) |
| = | 1200 | + | 120 | x | − | x | × | 20 | − | x | × | 2 | x |
| = | 1200 | + | 100 | x | − | x | × | 2 | x |
| 1200 | + | 100 | x | − | x | × | 2 | x | = | 2400 |