Wash. Rev. Code § 35.13.140
Whenever a petition for annexation is filed with the city or town council, or commission in those cities having a commission form of government, which meets the requirements herein specified, of which fact satisfactory proof may be required by the council or commission, the council or commission may entertain the same, fix a date for a public hearing thereon and cause notice of the hearing to be published in one issue of a newspaper of general circulation in the city or town. The notice shall also be posted in three public places within the territory proposed for annexation, and 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.
RCW 35.13.140
SLC-RO-8.