| 100 | − | ( | 10 | + | 10 | − | X | ) | × | 10 | ÷ | 2 | = | 375 2 | − | ( | 15 | + | X | ) | × | 15 | ÷ | 2 |
| Left side of the equation = | 100 | − | ( | 10 | + | 10 | − | X | ) | × | 5 |
| 100 | − | ( | 10 | + | 10 | − | X | ) | × | 5 | = | 375 2 | − | ( | 15 | + | X | ) | × | 15 | ÷ | 2 |
| Left side of the equation = | 100 | − | 10 | × | 5 | − | 10 | × | 5 | + | X | × | 5 |
| = | 100 | − | 50 | − | 50 | + | X | × | 5 |
| = | 0 | + | 5 | X |
| 0 | + | 5 | X | = | 375 2 | − | ( | 15 | + | X | ) | × | 15 | ÷ | 2 |
| Right side of the equation = | 375 2 | − | ( | 15 | + | X | ) | × | 15 2 |
| 0 | + | 5 | X | = | 375 2 | − | ( | 15 | + | X | ) | × | 15 2 |
| Right side of the equation = | 375 2 | − | 15 | × | 15 2 | − | X | × | 15 2 |
| = | 375 2 | − | 225 2 | − | X | × | 15 2 |
| = | 75 | − | 15 2 | X |
| 5 | X | = | 75 | − | 15 2 | X |
| 5 | X | + | 15 2 | X | = | 75 |
25 2 | X | = | 75 |
| X | = | 75 | ÷ | 25 2 |
| = | 75 | × | 2 25 |
| = | 3 | × | 2 |
| X | = | 6 |