If, however, a protest against such amendment, supplement or change is presented, duly signed and acknowledged by the owners of 20% or more of either the area of the lots included in such proposed change or of those immediately adjacent in the rear thereof, extending 100 feet therefrom or of those directly opposite thereto, extending 100 feet from the street frontage of such opposite lots, such amendment shall not be passed except by a favorable vote of all the members of the Board of Trustees.