(a)In a case referred to in clause (a) of sub-rule (1), the tax payable by the assessee on his total income of the previous year in which the salary is received in arrears or in advance or, in which the family pension is received in arrears (such salary or family pension being hereafter in this sub-rule referred to respectively as the additional salary or additional family pension, as the case may be, and such previous year being hereafter in this sub-rule referred to as the relevant previous year) shall be reduced by the amount, if any, by which the tax on the additional salary or additional family pension, calculated in the manner specified in clause (b), exceeds the tax or the aggregate tax on the additional salary or additional family pension, calculated in the manner specified in clause (c) or clause (d), as the case may be.