| ( | 180 | − | 50 | − | x | ) | + | ( | 180 | − | 30 | − | 40 | − | x | ) | = | 240 |
| Left side of the equation = | 180 | − | 50 | − | x | + | ( | 180 | − | 30 | − | 40 | − | x | ) |
| = | 130 | − | x | + | ( | 180 | − | 30 | − | 40 | − | x | ) |
| = | 130 | − | x | + | 180 | − | 30 | − | 40 | − | x |
| = | 240 | − | 2 | x |
| 240 | − | 2 | x | = | 240 |
| - | 2 | x | = | 240 | − | 240 |
| - | 2 | x | = | 0 |
| - | 0 | = | 2 | x |
| 2 | x | = | - | 0 |
| x | = | - | 0 | ÷ | 2 |
| = | - | 0 | × | 1 2 |
| x | = | 0 |