When owners of more than 50% of the frontage within a district or part of a district shall present to the Borough Council a duly signed petition for the amendment, change or modification of the regulations prescribed for said district or part thereof, the Borough Council shall act upon said petition within 120 days after the filing of said petition with the Borough Clerk. Said petition shall be accompanied by a map showing the lots, buildings and uses of property within the area for which the change of district is asked as well as of all the property within 100 feet therefrom, exclusive of street space. Said petition shall furthermore set forth the grounds or reasons for the proposed change. Any proposed amendment or change of district or part of district petitioned by owners shall be referred to the Planning Board for study and report. The Planning Board shall report back to the Borough Council its findings upon such proposed amendment or change within 60 days after the receipt of such reference.