If the petition for annexation filed with the board of commissioners complies with the requirements of law, as proved to the satisfaction of the board of commissioners, it may entertain the petition, fix the date for public hearing thereon, and cause notice of the hearing to be published in one issue of a newspaper of general circulation in the area proposed to be annexed and also posted in three public places within the area proposed for annexation. The notice shall specify the time and place of hearing and invite interested persons to appear and voice approval or disapproval of the annexation. The expense of publication and posting of the notice shall be borne by the signers of the petition.