What are the constraints and the objective function Adam is developing a rental housing and retail area. The housing area consists of efficiency apartments, duplexes, and single-family homes. Maximum demand by potential renters is estimated to be 300 efficiency apartments, 200 duplexes, and 500 single-family homes, but the number of duplexes must equal at least 50% of the number of efficiency apartments and single homes. Retail space is proportionate to the number of home units at the rates of at least 12 ft, 18 ft', and 20 ft for efficiency, duplex, and single-family units, respectively. However, land availability limits retail space to no more than 15,000 ft. The monthly rental income is estimated at $650, $800, and $1500 for efficiency-, duplex-, and single-family units, respectively. The retail space rents for $120/ ft. Develop an LP model to determine the optimal retail space area and the number of family residences.