The demand for a spare part is three per day, according to a Poisson distribution. The parts can be obtained from a tool crib, which stocks 3 spare parts each day. If the demand cannot be obtained from the tool crib, it must be obtained from central stores, at a considerable distance. Note that all demands are satisfied, either from the tool crib or from central stores. a.) What is the probability of having 2 demands in a day? b.) What is the probability that at least 1 part is obtained from central stores? c.)) What is the probability that all three parts stocked at the tool crib are used in a day? d.) What is the expected number of parts obtained from the tool crib daily? e.) What is the expected number of parts obtained from central stores in a given day? f.) How many spare parts should be kept at the tool crib to meet the daily demand least 90 percent of the time?