A special fund known as the “state retirement and investment fund” is established for the purpose of defraying administrative expenses of the state retirement and investment office. The actual amount of administrative expenses incurred by the state retirement and investment office must be paid from the respective funds listed under section 21-10-06 and are hereby appropriated to the state retirement and investment fund in proportion to the services rendered for each fund as estimated by the state investment board. The amount necessary to pay all administrative expenses of the state retirement and investment office must be paid from the state retirement and investment fund in accordance with the agency’s appropriation authority and earnings lawfully available for such purposes. Any interest income earned on the state retirement and investment fund must be credited to the fund.