Density. For specific project density computation, the allowable maximum unit density shall be determined by dividing the gross area of the planned development (exclusive of existing public right-of-way or public open space easement) by the square feet per family as required by the district intended. In the case of mixed-use developments, a separate density calculation shall be computed for each defined use in the development. (Example: On an eighty-acre planned development, 40 acres are intended for RM-1 uses and 40 acres are intended for RS-1 uses; the density computations would be run separately as follows: 1,742,400 square feet divided by 5,000 square feet per unit for RM-1 and 1,742,400 square feet divided by 30,000 square feet per unit for RS-1.)