Whenever the owners of 50% or more of the street frontage in any district or any specified part thereof shall present to the Board of Trustees a petition duly signed and acknowledged requesting an amendment, supplement, change, modification or repeal of the regulations prescribed for or the Zoning Maps, including said district or said specified part thereof, it shall be the duty of the Board of Trustees to hold a public hearing thereon and cause notice thereof to be given in the manner prescribed above.