At or before the issuance of any such bonds, the board shall, by resolution, provide for a sinking fund for the payment of the bonds and the interest thereon, and the payment of the charges of banks or trust companies for making payment of such bonds, and interest, out of the net revenues of said athletic establishment, and shall set aside and pledge a sufficient amount of the net revenues of the athletic establishment to be paid by the board into such sinking fund at intervals to be determined by resolution adopted prior to the issuance of the bonds, for: (a) The interest upon such bonds as the same becomes due; (b) the necessary fiscal agency charges for paying bonds and interest; (c) the payment of the bonds as they fall due, or if all bonds mature at one time, the maintenance of a proper sinking fund for the payment thereof at such time; and (d) a margin for safety and for the payment of premium upon bonds retired by call or purchase as herein provided for, which margin, together with unused surplus of such margin carried forward from the preceding year, shall equal ten per cent of all other amounts so required to be paid into the sinking fund. Such required payments shall constitute a first charge upon all the net revenues of the athletic establishment. Net revenues as used herein shall mean the revenues of the athletic establishment remaining after the payment of reasonable expense of operation, repairs, maintenance, insurance and all other reasonable costs of maintaining and operating the same required to be paid from the revenues thereof. After the payment into the sinking fund as herein required, the board may at any time in its discretion transfer all or any part of the balance of the net revenues, after reserving an amount deemed by the board sufficient for operation, repairs, maintenance and depreciation for an ensuing period of not less than twelve months, into the sinking fund or into a fund for extensions, improvements and additions to such athletic establishment. All amounts for sinking fund and interest, as and when set apart for the payment of same, shall be remitted to the West Virginia Municipal Bond Commission at such periods as shall be designated in the resolution, but in any event at least thirty days previous to the time interest or principal payments become due, to be retained and paid out by said commission, consistent with provisions of this article and the order pursuant to which such bonds have been issued. The West Virginia Municipal Bond Commission is hereby authorized to act as fiscal agent for the administration of such sinking fund under any resolution adopted pursuant to the provisions of this article and shall invest all sinking funds as provided by general law. Notwithstanding the foregoing, payments of principal and interest on any bonds owned by the United States or any governmental agency or department thereof may be made by the board directly thereto.