Whenever a petition, signed by qualified electors, in number equal to twenty percent of the votes cast at the last general or special municipal election, be presented to the Council accompanied by a proposed amendment to the charter, requesting that such proposed amendment be submitted to a vote of the people at the next general or special municipal election occurring forty-five (45) days or more after such petition is filed, and if approved by a majority of the electors voting upon it, such amendment shall become a part of this charter; provided, that when any amendment shall have been adopted by a vote of the people as in this section provided, the Mayor shall, within the next five (5) days, proclaim such amendment a part of this charter, and shall then cause such proclamation to be published in the City official newspaper; provided, further, that if more than one amendment be submitted at any election, they shall be submitted in such manner that each proposed amendment may be voted upon separately without prejudice to others.