Obviously if the model wants to upgrade the kitchen, it should be done by either the landlord or a subcontractor. as he creates the ip model, the landlord wants to leave the choice of whether to actually upgrade the kitchen up to the optimization algorithm. how should this constraint be written if he uses the following scheme for decision variables? 5 points
x1 = contractor works on wood floors x2 = landlord works on wood floorsx3 = contractor works on kitchen tile x4 = landlord on kitchen tilex5 = contractor works on back door x6 = landlord works on back doorx7 = contractor works on garage door x8 = landlord works on garage doora) x3 + x4 ≤ 1b) x3 + x4 = 1c) x3 - x4 ≤ 1d) x3 - x4 = 1