Lotus Point Project is a site construction project and both houses and flats will be built. The site can accommodate 10,000 residences as houses and flats. The project should include a recreation project: either a swimming-tennis complex or a sailing marina, but not both. If a marina is to be built, the number of houses in the project should be at least three times the number of apartments in the project. A swimming-tennis complex will cost $2.8 million, and a marina $1.2 million. The developers of the project believe that each house will generate $46,000 and each flat will generate $48,000. The cost of building a house or apartment would be $40,000. Formulate an IP (integer programming model) that will help Lotus Point maximize profits.