| 88 | X | + | ( | 90 | − | X | ) | × | 83 | = | 87 | × | 90 |
| Left side of the equation = | 88 | X | + | 90 | × | 83 | − | X | × | 83 |
| = | 88 | X | + | 7470 | − | X | × | 83 |
| = | 5 | X | + | 7470 |
| 5 | X | + | 7470 | = | 87 | × | 90 |
| Right side of the equation = | 7830 |
| 5 | X | + | 7470 | = | 7830 |
| 5 | X | = | 7830 | − | 7470 |
| 5 | X | = | 360 |
| X | = | 360 | ÷ | 5 |
| = | 360 | × | 1 5 |
| = | 72 | × | 1 |
| X | = | 72 |