A long solenoid with 1000 turns $/ \mathrm{m}$ has a core material with relative permeability 500 and volume $10^3 \mathrm{~cm}^3$. If the core material is replaced by another material having relative permeability of 750 with same volume maintaining same current of 0.75 A in the solenoid, the fractional change in the magnetic moment of the core would be approximately $\left(\frac{x}{599}\right)$ Find the value of x.