\( \mathrm{A_3B_2} \) is a sparingly soluble salt of molar mass \( M \) (\( \mathrm{g\, mol^{-1}} \)) and solubility \( x \) \( \mathrm{g\, L^{-1}} \). The solubility product satisfies \( K_{sp} = a \left( \frac{x}{M} \right)^{5} \). The value of \( a \) is ____________ . (Integer answer)
