42.0.18. Any method that a financial institution is required in accordance with any of sections 42.0.15 to 42.0.17 to use in respect of any of its fiscal years must be(1) fair and reasonable;
(2) used consistently by the financial institution throughout the fiscal year; and
(3) subject to section 42.0.19, determined by the financial institution no later than the day on which the financial institution is required to file the return provided for in Division IV of Chapter VIII for the first reporting period in the fiscal year.