Section 9. In the case of a petition for the adoption of Plan A, B, C, D or E, within seventy days after the petition has been filed with him by the petitioners the city clerk shall, except as provided in section ten, transmit a certified copy thereof to the city council, except that the signatures upon the petition need not be copied but in place thereof the city clerk shall state the number of signatures of registered voters thereon, certified as such by the registrars of voters. If any question arises as to the validity or sufficiency of the petition or of the signatures thereon, any registered voter of the city may appeal for a determination of said question to the applicable board referred to in section twelve of chapter fifty-three, by filing a notice of such appeal with the city council and with the clerk of the board of registrars of voters within eighty days after the date the petition was filed with the city clerk by the petitioners, and the board so appealed to shall within thirty days render a decision thereon. The board shall submit notice of its decision forthwith to the city council.

Any person aggrieved by the decision of the board under this section may appeal to the superior court sitting in equity, for the county in which the city is located; provided, that such appeal is filed in said court within ten days after such decision is rendered. It shall hear all pertinent evidence and determine the facts and, upon the facts as so determined, annul such decision if found to be erroneous in law or not warranted by the evidence, or make such other decree as justice and equity may require. The foregoing remedy shall be exclusive, but the parties shall have all rights of appeal and exception as in other equity cases.

No costs shall be allowed against the board unless the court finds that it acted with gross negligence or in bad faith.

Within ten days after the expiration of said period of eighty days, if no appeal has been taken, or after receipt of a decision on any appeal in favor of the validity or sufficiency of such petition or signatures, as the case may be, the city council shall, unless the number of valid signatures certified to it is found to be less than the number required by section seven, transmit such certified copy to the city clerk. If said certified copy is so transmitted to the city clerk at least thirty days before the regular city election, the question proposed by the petition shall be submitted upon the official ballot to a vote of the registered voters of the city at said regular city election, otherwise it shall be submitted at the regular city election next following the aforesaid election.