Wash. Rev. Code § 35A.14.297
On the date set for hearing as provided in RCW 35A.14.295, residents or property owners of the area included in the resolution for annexation shall be afforded an opportunity to be heard. The legislative body may provide by ordinance for annexation of the territory described in the resolution, but the effective date of the ordinance shall be not less than forty-five days after the passage thereof. The legislative body shall cause notice of the proposed effective date of the annexation, together with a description of the property to be annexed, to be published at least once each week for two weeks subsequent to passage of the ordinance, in one or more newspapers of general circulation within the city and in one or more newspapers of general circulation within the area to be annexed. If the annexation ordinance provides for assumption of indebtedness or adoption of a proposed zoning regulation, the notice shall include a statement of such requirements. Such annexation ordinance shall be subject to referendum for forty-five days after the passage thereof. Upon the filing of a timely and sufficient referendum petition as provided in RCW 35A.14.299 below, a referendum election shall be held as provided in RCW 35A.14.299, and the annexation shall be deemed approved by the voters unless a majority of the votes cast on the proposition are in opposition thereto. After the expiration of the forty-fifth day from, but excluding the date of passage of the annexation ordinance, if no timely and sufficient referendum petition has been filed, as provided by RCW 35A.14.299 below, the area annexed shall become a part of the code city upon the date fixed in the ordinance of annexation.
RCW 35A.14.297