The bids shall be in writing, sealed and filed with the city clerk prior to the time they are to be opened and the bids shall be opened at the time specified in the notice, at which time any or all bids may be rejected, or the mayor may readvertise for bids, or after due consideration thereof may award a contract to, or purchase such supplies, materials or equipment from, the lowest and best responsible bidder. (Prior code §8-4)