$A _{2} X \rightarrow 2 A ^{+}+ X ^{2-}$

$2 S _{1} \quad S _{1}$

$K _{ sp }=4 S _{1}^{3}=4 \times 10^{-12}$

$S _{1}=10^{-4}$

for $MX$

$MX \rightarrow M ^{+}+ X ^{-}$

$\begin{array}{ll} S _{2}  S _{2}\end{array}$

$K _{ sp }= S _{2}^{2}=4 \times 10^{-12}$

$S _{2}=2 \times 10^{-6}$

so $\frac{ S _{ A _{2} x }}{ S _{ MX }}=\frac{10^{-4}}{2 \times 10^{-6}}=50$