(ii)one-third of the amount referred to in section 180 included in the total income of the previous year aforesaid shall be included in the total income of each of the two next succeeding previous years and the tax payable, if any, in respect of each of the assessments relevant to the two said succeeding previous years shall be reduced by an amount equal to one-half of the tax referred to in sub-clause (b) of clause (i).