Explanation

Given x - 1/2x} = 6,

Cubing both sides gives x^3 - 1/8x^3 - 3.1/2.6 = 216.

This simplifies to x^3 - 1/8x^3 - 9 = 216.

So, x^3 - 1/8x^3 = 216 + 9 = 225.