Density of development. An adult multifamily development shall be permitted at a density of eight units per acre, and further provided that the Planning Board may permit the density to increase to a maximum of 12 units per acre, subject to the following formula: An increase of one-unit-per-acre density or fraction thereof up to a maximum of a three-unit-per-acre increase shall be permitted for each increment of land area to provide for the equivalent of 100 off-street commuter parking spaces provided. Such land shall be dedicated to the Township of Manalapan. Fractional computation of density increase shall be permitted.