According to question,
Cost of one m³ of cloth = Rs 500
Cost of the cube =256 RS
Therefore, volume of the cube = cost of the cube/ cost of 1m³ of cloth
Now to convert it into cm³ we multiply 1000000 to it.
Thus, 0.512m³ = 0.512 x 1000000 = 512000cm³
So we have the volume as 512000cm³. Thus the length of the side of the cube = ∛512000
Hope that helps !!