| ( | 21 | − | 3 | x | ) | ( | 8 | − | 2 | x | ) | = | 60 |
| Left side of the equation = | 21 | ( | 8 | − | 2 | x | ) | − | 3 | x | ( | 8 | − | 2 | x | ) |
| = | 21 | × | 8 | − | 21 | × | 2 | x | − | 3 | x | ( | 8 | − | 2 | x | ) |
| = | 168 | − | 42 | x | − | 3 | x | ( | 8 | − | 2 | x | ) |
| = | 168 | − | 42 | x | − | 3 | x | × | 8 | + | 3 | x | × | 2 | x |
| = | 168 | − | 42 | x | − | 24 | x | + | 6 | x | x |
| = | 168 | − | 66 | x | + | 6 | x | x |
| 168 | − | 66 | x | + | 6 | x | x | = | 60 |