If the contractor has furnished the district all required records and reports, the district shall after July 10, 1984, pay the contractor interest at the rate specified in section 39-1349, as such rate may from time to time be adjusted by the Legislature, on any contract amount retained and the final payment due the contractor beginning twenty days after completion of the work covered by the contract under section 31-748. The contractor shall notify the district in writing that the work has been completed and the district, within twenty days after receipt of such notice, shall give written notice to the contractor of any objections by the district to acceptance of the work.