| ( | 120 | − | a | ) | ( | 64 | + | 8 5 | a | ) | = | 8800 |
| Left side of the equation = | 120 | ( | 64 | + | 8 5 | a | ) | − | a | ( | 64 | + | 8 5 | a | ) |
| = | 120 | × | 64 | + | 120 | × | 8 5 | a | − | a | ( | 64 | + | 8 5 | a | ) |
| = | 7680 | + | 192 | a | − | a | ( | 64 | + | 8 5 | a | ) |
| = | 7680 | + | 192 | a | − | a | × | 64 | − | a | × | 8 5 | a |
| = | 7680 | + | 128 | a | − | a | × | 8 5 | a |
| 7680 | + | 128 | a | − | a | × | 8 5 | a | = | 8800 |