| 12000 | + | 15 | ( | X | − | 1000 | ) | − | 4000 | + | ( | 4 | + | 1 | ) | X | = | 0 |
| Left side of the equation = | 8000 | + | 15 | ( | X | − | 1000 | ) | + | ( | 4 | + | 1 | ) | X |
| 8000 | + | 15 | ( | X | − | 1000 | ) | + | ( | 4 | + | 1 | ) | X | = | 0 |
| Left side of the equation = | 8000 | + | 15 | X | − | 15 | × | 1000 | + | ( | 4 | + | 1 | ) | X |
| = | 8000 | + | 15 | X | − | 15000 | + | ( | 4 | + | 1 | ) | X |
| = | - | 7000 | + | 15 | X | + | ( | 4 | + | 1 | ) | X |
| = | - | 7000 | + | 15 | X | + | 4 | X | + | 1 | X |
| = | - | 7000 | + | 20 | X |
| - | 7000 | + | 20 | X | = | 0 |
| 20 | X | = | 0 | + | 7000 |
| 20 | X | = | 7000 |
| X | = | 7000 | ÷ | 20 |
| = | 7000 | × | 1 20 |
| = | 350 | × | 1 |
| X | = | 350 |