| ( | 20 | − | 2 | X | ) | ( | 10 | − | 2 | X | ) | = | 128 |
| Left side of the equation = | 20 | ( | 10 | − | 2 | X | ) | − | 2 | X | ( | 10 | − | 2 | X | ) |
| = | 20 | × | 10 | − | 20 | × | 2 | X | − | 2 | X | ( | 10 | − | 2 | X | ) |
| = | 200 | − | 40 | X | − | 2 | X | ( | 10 | − | 2 | X | ) |
| = | 200 | − | 40 | X | − | 2 | X | × | 10 | + | 2 | X | × | 2 | X |
| = | 200 | − | 40 | X | − | 20 | X | + | 4 | X | X |
| = | 200 | − | 60 | X | + | 4 | X | X |
| 200 | − | 60 | X | + | 4 | X | X | = | 128 |