| ( | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 2520 | ) | − | ( | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 1410 | ) | = | 4000 |
| Left side of the equation = | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 2520 | − | ( | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 1410 | ) |
| = | X | × | 12 | − | ( | 5000 | + | 1500 | + | 2000 | ) | × | 12 | − | 2520 | − | ( | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 1410 | ) |
| = | 12 | X | − | 5000 | × | 12 | − | 1500 | × | 12 | − | 2000 | × | 12 | − | 2520 | − | ( | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 1410 | ) |
| = | 12 | X | − | 60000 | − | 18000 | − | 24000 | − | 2520 | − | ( | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 1410 | ) |
| = | 12 | X | − | 104520 | − | ( | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | − | 1410 | ) |
| = | 12 | X | − | 104520 | − | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 | + | 1410 |
| = | 12 | X | − | 103110 | − | ( | X | − | ( | 5000 | + | 1500 | + | 2000 | ) | ) | × | 12 |
| = | 12 | X | − | 103110 | − | X | × | 12 | + | ( | 5000 | + | 1500 | + | 2000 | ) | × | 12 |
| = | 0 | X | − | 103110 | + | ( | 5000 | + | 1500 | + | 2000 | ) | × | 12 |
| = | 0 | X | − | 103110 | + | 5000 | × | 12 | + | 1500 | × | 12 | + | 2000 | × | 12 |
| = | 0 | X | − | 103110 | + | 60000 | + | 18000 | + | 24000 |
| = | 0 | X | − | 1110 |
| 0 | X | − | 1110 | = | 4000 |
| = | 4000 | + | 1110 |