110. Determination of tax where total income includes income on which no tax is payableWhere there is included in the total income of an assessee any income on which no income-tax is payable under the provisions of this Act, the assessee shall be entitled to a deduction, from the amount of income-tax with which he is chargeable on his total income, of an amount equal to the income-tax calculated at the average rate of income-tax on the amount on which no income-tax is payable.