Except as provided in section 28, every county college shall, on an annual basis or at such lesser intervals as may be fixed by it, solicit by public advertisement the submission of bids for the furnishing of all work, materials and supplies which are and which under section 4 can be purchased or agreed or contracted to be furnished only after public advertising for bids and bidding therefor.
N.J.S. § 18A:64A-25.8