If an initiative petition or amended petition, be found sufficient by the city clerk he shall immediately so certify and promptly submit the proposed ordinance therein set forth to the commission which shall at once read it and refer it to an appropriate committee, which may be a committee of the whole. Provision shall be made for public hearings upon the proposed ordinance before the committee to which it is referred. Thereafter the committee shall report the proposed ordinance to the commission, with its recommendations thereon, not later than sixty days after the date on which it was submitted to the commission by the city clerk. Upon receiving the proposed ordinance from the committee, the commission shall proceed at once to consider it and to take final action thereon within thirty days from the date of such committee report.