| ( | x | − | 30 | ) | ( | 280 | − | ( | x | − | 40 | ) | ) | = | 2610 |
| Left side of the equation = | x | ( | 280 | − | ( | x | − | 40 | ) | ) | − | 30 | ( | 280 | − | ( | x | − | 40 | ) | ) |
| = | x | × | 280 | − | x | ( | x | − | 40 | ) | − | 30 | ( | 280 | − | ( | x | − | 40 | ) | ) |
| = | 280 | x | − | x | x | + | x | × | 40 | − | 30 | ( | 280 | − | ( | x | − | 40 | ) | ) |
| = | 320 | x | − | x | x | − | 30 | ( | 280 | − | ( | x | − | 40 | ) | ) |
| = | 320 | x | − | x | x | − | 30 | × | 280 | + | 30 | ( | x | − | 40 | ) |
| = | 320 | x | − | x | x | − | 8400 | + | 30 | ( | x | − | 40 | ) |
| = | 320 | x | − | x | x | − | 8400 | + | 30 | x | − | 30 | × | 40 |
| = | 320 | x | − | x | x | − | 8400 | + | 30 | x | − | 1200 |
| = | 350 | x | − | x | x | − | 9600 |
| 350 | x | − | x | x | − | 9600 | = | 2610 |