The stoichiometry and solubility product of a salt

From the graph \& dimensions salt is : $\mathrm{XY}_{2}$

${[\mathrm{X}]=1 \times 10^{-3} \mathrm{M} }$

${[\mathrm{Y}]=2 \times 10^{-3} \mathrm{M} }$

$\mathrm{XY}_{2}(\mathrm{~s}) \rightleftharpoons \mathrm{X}_{(\mathrm{aq})}^{2+}+2 \mathrm{Y}_{(\mathrm{aq} .)}^{-}$

$\mathrm{ksp}=\left[\mathrm{X}^{2+}\right]\left[\mathrm{Y}^{-}\right]^{2}$

$=\left(10^{-3}\right)\left(2 \times 10^{-3}\right)^{2}$

$=4 \times 10^{-9} \mathrm{M}^{3}$