Every cooperative electrical association in this state shall file with the state tax commission of the state of Idaho the operators’ statement provided for in section 63-404, Idaho Code, and shall include thereon a statement of the amount of its gross earnings for the calendar year next preceding. Upon examining and verifying said statement, the state tax commission shall compute the amount of the tax measured by the gross earnings and shall allot to each county in which the property of such association is situated, and otherwise exempted from taxation by section 63-602JJ, Idaho Code, that proportion of the total tax of such association shown to be due as the number of wire miles of transmission and distribution lines of such association situated in such county bears to the total wire miles of transmission and distribution lines of such association. The state tax commission shall then, for each county, apportion the tax so allotted to the county among the several taxing units thereof within which any property of such association is situated, and otherwise exempted from taxation by section 63-602JJ, Idaho Code, by apportioning to each such taxing unit that proportion of the tax so allotted to the county as the weighted wire mileage factor for each such taxing unit bears to the total of the weighted wire mileage factors of all such taxing units in the county. No later than the third Monday of May each year, the state tax commission shall notify the state superintendent of public instruction and the county treasurer of such allotment and apportionment and the amounts thereof.