| ( | 80 | − | 4 | x | ) | ( | 78 | − | 3 | x | ) | = | 864 |
| Left side of the equation = | 80 | ( | 78 | − | 3 | x | ) | − | 4 | x | ( | 78 | − | 3 | x | ) |
| = | 80 | × | 78 | − | 80 | × | 3 | x | − | 4 | x | ( | 78 | − | 3 | x | ) |
| = | 6240 | − | 240 | x | − | 4 | x | ( | 78 | − | 3 | x | ) |
| = | 6240 | − | 240 | x | − | 4 | x | × | 78 | + | 4 | x | × | 3 | x |
| = | 6240 | − | 240 | x | − | 312 | x | + | 12 | x | x |
| = | 6240 | − | 552 | x | + | 12 | x | x |
| 6240 | − | 552 | x | + | 12 | x | x | = | 864 |