| ( | 15 | − | 2 | x | ) | ( | 20 | − | 2 | x | ) | = | 246 |
| Left side of the equation = | 15 | ( | 20 | − | 2 | x | ) | − | 2 | x | ( | 20 | − | 2 | x | ) |
| = | 15 | × | 20 | − | 15 | × | 2 | x | − | 2 | x | ( | 20 | − | 2 | x | ) |
| = | 300 | − | 30 | x | − | 2 | x | ( | 20 | − | 2 | x | ) |
| = | 300 | − | 30 | x | − | 2 | x | × | 20 | + | 2 | x | × | 2 | x |
| = | 300 | − | 30 | x | − | 40 | x | + | 4 | x | x |
| = | 300 | − | 70 | x | + | 4 | x | x |
| 300 | − | 70 | x | + | 4 | x | x | = | 246 |