${\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]}^{3-}$ In this the central metal Fe is in +3 oxidation state. And ${\mathrm{CN}}^{-}$ is strong field ligand so, it will form inner orbital complex.

Electronic configuration in ${\mathrm{Fe}}^{3+}$: ${\mathrm{d}}^5$

Electronic configuration for inner orbital complex: ${{\mathrm{t}}^5}_{2\mathrm{g}} {{\mathrm{e}}^0}_{\mathrm{g}}$

$\mathrm{CFSE}=5\left(-0.4{\mathrm{\Delta }}_0\right)=-2.0{\mathrm{\Delta }}_0$

So, final answer will be $=2$