The area or areas to be included in the district must contain the territory described in the petition for the creation or modification thereof. However, the council, upon its own motion or upon the request of the board of commissioners, shall consider and may include within the boundaries of the district areas which may be benefited by being included therein. Upon a request by the board of commissioners to expand an existing district, the council shall hold a    hearing and investigation and file any order expanding a district in a manner similar to that provided in sections 23-24-02 and 23-24-04.