(a) Any bonds issued for refunding purposes may either be delivered in exchange for the outstanding bonds being refunded or may be publicly or privately sold.
(b) The refunding bonds, or any part thereof, may be exchanged by the board for investments under W.S. 21-17-426 which have been made available for escrow investment by any purchaser of refunding bonds, upon terms of exchange mutually agreed upon, and any such investments so received by the board shall be placed in escrow as provided by W.S. 21-17-440 and 21-17-441.