Where a lot is bounded by more than one street or private road, the front setback requirement shall apply to all sides adjacent to the streets or private roads except, however, in the R-4 and R-5 Zones which shall use the minimum front setback from the side with the least street frontage and use the following setback from the street with the greater frontage: R-4 Zone, the greater of 30 feet or the result of subtracting 45 feet from the lot width perpendicular to the side of the lot with the longer street frontage, but the latter need not exceed the normal front yard setback; R-5 Zone, the greater of 15 feet or the result of subtracting 35 feet from the lot width perpendicular to the side of the lot with the longer street frontage, but the latter need not exceed the normal front yard setback. The other remaining sides which are not bounded by a street shall be considered as side yards with the applicable requirement for that zone.