Upon receipt of the certified copy of a proposed ordinance and the additional petition presented in accordance with the foregoing section from the committee of the petitioners, the city secretary shall, if the city secretary finds the additional petition sufficient, certify that fact to the commission at its next regular meeting. When an initiative petition has been finally determined sufficient, the city commission shall promptly consider the proposed initiative ordinance in the manner prescribed for enacting ordinances. The city commission shall either adopt the ordinance proposed within thirty (30) days thereafter, or it shall submit such proposed ordinance to the voters at the next election date authorized under state law. If when submitted to the voters, a majority of those voting on a proposed ordinance shall vote in favor thereof, it shall thereupon be an ordinance of the municipality.