Upon the date fixed in the ordinance of annexation the area annexed shall become part of the city. All property within the territory hereafter annexed shall, if the annexation petition so provided, be assessed and taxed at the same rate and on the same basis as the property of such annexing code city is assessed and taxed to pay for the portion of any then-outstanding indebtedness of the city to which said area is annexed, which indebtedness has been approved by the voters, contracted for, or incurred prior to, or existing at, the date of annexation and that the city has required to be assumed. If the annexation petition so provided, all property in the annexed area shall be subject to and a part of the proposed zoning regulation as prepared and filed as provided for in RCW
35A.14.330 and
35A.14.340.