The chemical equation that has to be balanced is: K4Fe(CN)6 + H2SO4 + H2O = K2SO4 + FeSO4 + (NH4)2SO4 + CO
Go about doing this in the following manner:
Consider the first compound K4Fe(CN)6, K is present in only one of the compounds on the left. So you can write the coefficient of K2SO4 as 2. Similarly, considering Fe and N, we get the coefficients of FeSO4 as 1 and (NH4)2SO4 as 3.
As K2SO4, FeSO4 and (NH4)2SO4 have SO4 and we get 6 SO4 in total we can make the coefficient of H2SO4 as 6. (NH4)2SO4 has 8 H atoms and there are 3 of them, this gives 24 H atoms. From 6 H2SO4 we get 12 H atoms, the rest or 12 more come from the H20, so H2O can be given a coefficient of 6. Finally, there are 6 C atoms in K4Fe(CN)6, to accommodate this give CO a coefficient of 6. We finally get:
K4Fe(CN)6 + 6 H2SO4 + 6 H2O = 2 K2SO4 + FeSO4 + 3 (NH4)2SO4 + 6 CO