10 100 | x | + | 30 100 | ( | 800 | − | x | ) | = | 12 100 | × | 3000 |
| Left side of the equation = | 10 100 | x | + | 30 100 | × | 800 | − | 30 100 | x |
| = | 10 100 | x | + | 240 | − | 30 100 | x |
| = | - | 1 5 | x | + | 240 |
| - | 1 5 | x | + | 240 | = | 12 100 | × | 3000 |
| Right side of the equation = | 360 |
| - | 1 5 | x | + | 240 | = | 360 |
| - | 1 5 | x | = | 360 | − | 240 |
| - | 1 5 | x | = | 120 |
| - | 120 | = | 1 5 | x |
1 5 | x | = | - | 120 |
| x | = | - | 120 | ÷ | 1 5 |
| = | - | 120 | × | 5 |
| x | = | - | 600 |