The solubility of sparingly soluble salt $\mathrm{A}_{3} \mathrm{~B}_{2}$ (molar mass $=$ 'M' $\mathrm{g} / \mathrm{mol}$ ) in water is 'x' g/L. The ratio of molar concentration of $\mathrm{B}^{3}$ to the solubility product of the salt is
(a) $\frac{108 x^{5}}{M^{5}}$
(b) $\frac{x^{4}}{108 M^{4}}$
(c) $\frac{x^{4}}{54 M^{4}}$
(d) $\frac{x^{3}}{27 M^{3}}$