Write the half reactions

Write the half reactions for each of the following reactions and label each as an oxidation or reduction.
a) Mn2+ (aq) + BiO3 (aq) > MnO4 (aq) + Bi3+ (aq)b) CrO42- (aq) + HSnO2 (aq) + H2O (l) > CrO2 (aq) +HSnO3 (aq) + OH (aq)c) HBr (aq) + Fe