How to calculate the oxidation number of Iron in ferric ferrocyanide Fe₄[Fe(CN)₆]₃?

The dissociation of Fe4[Fe(CN)6]3 can be written as

Fe4[Fe(CN)6]3 → 4 Fe³⁺ + 3 [Fe(CN)6]^4-

Hence, the oxidation state of outer Fe is +3

Let the oxidation number of Fe be X

Here oxidation number on CN = -1

For [Fe(CN)6]^4-

X × 6 (-1) = -4

∴ X = +2, the oxidation state of inner Fe.