| ( | 160 | + | 40 | x | ) | ( | 120 | − | 10 | x | ) | = | 0 |
| Left side of the equation = | 160 | ( | 120 | − | 10 | x | ) | + | 40 | x | ( | 120 | − | 10 | x | ) |
| = | 160 | × | 120 | − | 160 | × | 10 | x | + | 40 | x | ( | 120 | − | 10 | x | ) |
| = | 19200 | − | 1600 | x | + | 40 | x | ( | 120 | − | 10 | x | ) |
| = | 19200 | − | 1600 | x | + | 40 | x | × | 120 | − | 40 | x | × | 10 | x |
| = | 19200 | − | 1600 | x | + | 4800 | x | − | 400 | x | x |
| = | 19200 | + | 3200 | x | − | 400 | x | x |
| 19200 | + | 3200 | x | − | 400 | x | x | = | 0 |