(5) The annexation ordinances provided for in *RCW 35.13.470(4) and subsection (4) of this section are subject to referendum for forty-five days after passage. Upon the filing of a timely and sufficient referendum petition with the legislative body, signed by registered voters in number equal to not less than fifteen percent of the votes cast in the last general state election in the area to be annexed, the question of annexation shall be submitted to the voters of the area in a general election if one is to be held within ninety days or at a special election called for that purpose according to RCW 29A.04.330. Notice of the election shall be given as provided in RCW 35.13.080 and the election shall be conducted as provided in the general election law. 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, the area annexed shall become a part of the city or town upon the date fixed in the ordinance of annexation.