| 2160 | + | ( | 12 | − | x | ) | ( | 180 | − | 10 | x | ) | = | 4160 |
| Left side of the equation = | 2160 | + | 12 | ( | 180 | − | 10 | x | ) | − | x | ( | 180 | − | 10 | x | ) |
| = | 2160 | + | 12 | × | 180 | − | 12 | × | 10 | x | − | x | ( | 180 | − | 10 | x | ) |
| = | 2160 | + | 2160 | − | 120 | x | − | x | ( | 180 | − | 10 | x | ) |
| = | 4320 | − | 120 | x | − | x | ( | 180 | − | 10 | x | ) |
| = | 4320 | − | 120 | x | − | x | × | 180 | + | x | × | 10 | x |
| = | 4320 | − | 300 | x | + | x | × | 10 | x |
| 4320 | − | 300 | x | + | x | × | 10 | x | = | 4160 |