4 H2SO4 (aq) + KMnO4 (aq) + 5 K4Fe(CN)6 (aq) → 5 K3Fe(CN)6 (aq) + MnSO4 (aq) + 3 K2SO4 (aq) + 4 H2O (l)
This is an oxidation-reduction (redox) reaction:
MnVII + 5 e- → MnII (reduction)
5 FeII - 5 e- → 5 FeIII (oxidation)
KMnO4 is an oxidizing agent, K4Fe(CN)6 is a reducing agent.