Except as provided in RCW
35A.11.090, and except that the number of registered voters needed to sign a petition for initiative or referendum shall be fifteen percent of the total number of names of persons listed as registered voters within the city on the day of the last preceding city general election, the powers of initiative and referendum in noncharter code cities shall be exercised in the manner set forth for the commission form of government in RCW
35.17.240 through
35.17.360, as now or hereafter amended.