A town has 15 sections (shown in attached file) and in each section a firefighting unit operates. During summer some units have to leave the town to go to other towns. Which is the minimum required number of units that must stay in the town so that it is safe. Each unit can cover the specific area of the section that it is located and also the section that neighbors with it. The answer must be given in linear programming form (minZ=....... and the restrictions that describe it)