| 5 | ( | 5 | ( | 5 | X | + | 1 | ) | + | 1 | ) | + | 1 | = | 131 |
| Left side of the equation = | 5 | × | 5 | ( | 5 | X | + | 1 | ) | + | 5 | × | 1 | + | 1 |
| = | 25 | ( | 5 | X | + | 1 | ) | + | 5 | + | 1 |
| = | 25 | ( | 5 | X | + | 1 | ) | + | 6 |
| = | 25 | × | 5 | X | + | 25 | × | 1 | + | 6 |
| = | 125 | X | + | 25 | + | 6 |
| = | 125 | X | + | 31 |
| 125 | X | + | 31 | = | 131 |
| 125 | X | = | 131 | − | 31 |
| 125 | X | = | 100 |
| X | = | 100 | ÷ | 125 |
| = | 100 | × | 1 125 |
| = | 4 | × | 1 5 |
| X | = | 4 5 |
| X | = | 0.8 |