Where two returns are required to be filed as provided in section 77-2765:

(1) Personal exemptions and deductions shall be prorated between the two returns, under regulations prescribed by the Tax Commissioner, to reflect the proportions of the taxable year during which the individual was a resident and a nonresident; and

(2) The total of the taxes due thereon shall not be less than would be due if the total of the taxable incomes reported on the two returns were includable in one return.