If the board of supervisors determines, with respect to a petition for additional lights filed in conformity with this chapter, that
(a)
It is just and equitable, and in the public interest, that the proposed temporary zone be formed, and
(b)
The petition was signed by resident taxpayers representing 60 percent or more of the total assessed valuation of all taxable property within the territory proposed to be formed into a zone,
the board shall by resolution, entered in its minutes, fix and describe the boundaries of the proposed zone in such manner that any territory which will not be benefited by inclusion therein, or which is not contiguous thereto, or which is not described in the petition, shall not be included therein; shall declare the zone established, designating it by an identifying name or number; and shall specify the purposes and duration thereof, not to exceed three years from the beginning of the next ensuing fiscal year in which a special tax levy or assessment may be made in the zone.