If a tract of land 10 acres or greater in area is being subdivided or resubdivided into lots, it may be developed with a minimum average lot size of 8,400 square feet; minimum lot sizes of 7,200 square feet; and minimum lot widths of 60 feet. For the purpose of meeting the average lot size requirement, lots with more area than 10,000 square feet shall be calculated as having 10,000 square feet.