| 180 | − | 30 | − | ( | 40 | − | x | ) | + | 180 | − | 50 | − | x | = | 360 | − | 180 | − | 60 |
| Left side of the equation = | 280 | − | ( | 40 | − | x | ) | − | x |
| 280 | − | ( | 40 | − | x | ) | − | x | = | 360 | − | 180 | − | 60 |
| Left side of the equation = | 280 | − | 40 | + | x | − | x |
| = | 240 | + | 0 | x |
| 240 | + | 0 | x | = | 360 | − | 180 | − | 60 |
| Right side of the equation = | 120 |
| 240 | + | 0 | x | = | 120 |
| = | 120 | − | 240 |