| 240 | = | ( | 180 | − | ( | 50 | − | ( | 40 | − | x | ) | ) | ) | + | ( | 180 | − | 30 | − | x | ) |
| Right side of the equation = | 180 | − | ( | 50 | − | ( | 40 | − | x | ) | ) | + | ( | 180 | − | 30 | − | x | ) |
| = | 180 | − | 50 | + | ( | 40 | − | x | ) | + | ( | 180 | − | 30 | − | x | ) |
| = | 130 | + | ( | 40 | − | x | ) | + | ( | 180 | − | 30 | − | x | ) |
| = | 130 | + | 40 | − | x | + | ( | 180 | − | 30 | − | x | ) |
| = | 170 | − | x | + | ( | 180 | − | 30 | − | x | ) |
| = | 170 | − | x | + | 180 | − | 30 | − | x |
| = | 320 | − | 2 | x |
| 240 | = | 320 | − | 2 | x |
| 2 | x | = | 320 | − | 240 |
| 2 | x | = | 80 |
| x | = | 80 | ÷ | 2 |
| = | 80 | × | 1 2 |
| = | 40 | × | 1 |
| x | = | 40 |