A hurricane evacuation shelter, operating the local municipality, wants to be sure (99.9%) they will have power for up to a 3 week period where the power is provided using generators. After a search of the market no single generator was found that could provide the required 1 reliability, so instead multiple generators will be purchased and operated in an active parallel arrangement. An analyst for the municipality identified a generator from one supplier that has a reliability of 0.7 over a 3-week period. How many generators of this type are required to meet the design requirement