The board shall advertise for bids by at least two insertions, not less than five days apart, in a newspaper of general circulation circulated within the district, or if there is none, shall post notice at least 10 days before the date of opening of bids in at least three public places in the district that have been designated by resolution of the district as the places for posting public notices. The notice inviting sealed bids shall state the proposed improvement or work and shall set a date for opening of bids.