a) Consider a four link supply chain with the following data: Link 1 - using rail - lead time range 4-6 days, Link 2 - using water - lead time 15-21 days, Link 3 - using rail - Lead time 3-5 days, Link 4 - using truck lead time 2-4 days. The material enters North America from overseas supplier at the end of link 2. Daily demand is 500 units with no demand uncertainty. Treat each range as a measure of 6 sigma variation. Use a service level of 0.98 and estimates safety stock to be carried by the customer. b) compare the in-transit inventory and the safety with another supplier who can supply by road with a lead time with a range of 1-2 days. c) select a measure of risk and estimate it for each of the two supply chains.