| ( | 16 | − | a | ) | ( | 160 | + | 120 | a | ) | = | 3640 |
| Left side of the equation = | 16 | ( | 160 | + | 120 | a | ) | − | a | ( | 160 | + | 120 | a | ) |
| = | 16 | × | 160 | + | 16 | × | 120 | a | − | a | ( | 160 | + | 120 | a | ) |
| = | 2560 | + | 1920 | a | − | a | ( | 160 | + | 120 | a | ) |
| = | 2560 | + | 1920 | a | − | a | × | 160 | − | a | × | 120 | a |
| = | 2560 | + | 1760 | a | − | a | × | 120 | a |
| 2560 | + | 1760 | a | − | a | × | 120 | a | = | 3640 |