| 80 | x | + | 1080 | = | 100 | ( | x | − | 400 | ) |
| Right side of the equation = | 100 | x | − | 100 | × | 400 |
| = | 100 | x | − | 40000 |
| 80 | x | + | 1080 | = | 100 | x | − | 40000 |
| 80 | x | − | 100 | x | = | - | 40000 | − | 1080 |
| - | 20 | x | = | - | 40000 | − | 1080 |
| - | 20 | x | = | - | 41080 |
| 41080 | = | 20 | x |
| 20 | x | = | 41080 |
| x | = | 41080 | ÷ | 20 |
| = | 41080 | × | 1 20 |
| = | 2054 | × | 1 |
| x | = | 2054 |