| ( | 28 | − | 2 | x | ) | ( | 12 | − | 2 | x | ) | = | 198 |
| Left side of the equation = | 28 | ( | 12 | − | 2 | x | ) | − | 2 | x | ( | 12 | − | 2 | x | ) |
| = | 28 | × | 12 | − | 28 | × | 2 | x | − | 2 | x | ( | 12 | − | 2 | x | ) |
| = | 336 | − | 56 | x | − | 2 | x | ( | 12 | − | 2 | x | ) |
| = | 336 | − | 56 | x | − | 2 | x | × | 12 | + | 2 | x | × | 2 | x |
| = | 336 | − | 56 | x | − | 24 | x | + | 4 | x | x |
| = | 336 | − | 80 | x | + | 4 | x | x |
| 336 | − | 80 | x | + | 4 | x | x | = | 198 |