| ( | 30 | − | 3 | x | ) | ( | 36 | − | x | ) | = | 1560 |
| Left side of the equation = | 30 | ( | 36 | − | x | ) | − | 3 | x | ( | 36 | − | x | ) |
| = | 30 | × | 36 | − | 30 | x | − | 3 | x | ( | 36 | − | x | ) |
| = | 1080 | − | 30 | x | − | 3 | x | ( | 36 | − | x | ) |
| = | 1080 | − | 30 | x | − | 3 | x | × | 36 | + | 3 | x | x |
| = | 1080 | − | 30 | x | − | 108 | x | + | 3 | x | x |
| = | 1080 | − | 138 | x | + | 3 | x | x |
| 1080 | − | 138 | x | + | 3 | x | x | = | 1560 |