At the option of the developer, up to forty (40%) percent of the gross residential tract area, as defined in subsection 37-44.7 herein, may be developed with townhouse style dwelling units at a maximum density of ten (10) dwelling units per acre on the portion of the tract devoted to such development, provided the density of the portion of the tract devoted to multifamily (apartment) dwellings does not exceed fourteen (14) units per acre and further provided that the forty-five (45) multifamily (apartment) affordable rental units that would have derived from the construction of the entire gross residential tract area with multifamily (apartment) dwellings will still be constructed, regardless of any reduction in the total number of dwelling units in the development due to the developer's exercise of this townhouse option.