(a) General.-The tax imposed by section two, with any modification permitted by subdivision (b) of this section, is imposed for each taxable year beginning with taxable years ending after July first, nineteen hundred sixty-six and prior to January first, nineteen hundred seventy-six and each taxable year beginning in nineteen hundred seventy-five and ending in nineteen hundred seventy-six. (b) Alternate methods for determining tax for taxable years ending on or after July first, nineteen hundred