limiting factor analysis

Because there is no point in producing more than can be sold. Limited demand automatically creates a limit on the number of units that will be produced. You clearly have not watched my free lectures on linear programming because the example I work through has limited demand (as do most questions in the exam). You really cannot expect me to spend time answering your questions if you are not prepared to spend time watching my lectures - I am certainly not going to type out my lectures here :-)