| ( | 120 | − | x | ) | ( | 160 | + | 2 | x | ) | = | 20000 |
| Left side of the equation = | 120 | ( | 160 | + | 2 | x | ) | − | x | ( | 160 | + | 2 | x | ) |
| = | 120 | × | 160 | + | 120 | × | 2 | x | − | x | ( | 160 | + | 2 | x | ) |
| = | 19200 | + | 240 | x | − | x | ( | 160 | + | 2 | x | ) |
| = | 19200 | + | 240 | x | − | x | × | 160 | − | x | × | 2 | x |
| = | 19200 | + | 80 | x | − | x | × | 2 | x |
| 19200 | + | 80 | x | − | x | × | 2 | x | = | 20000 |