Suppose you are a corporate buyer. One of your suppliers delivers a particular part in 12 days on average, with a standard deviation of 3. The daily usage averages 20 units per day with a standard deviation of 4. What is the standard deviation of demand during lead-time? If you use a continuous review policy, how much safety stock would you want on hand to ensure at least 90 percent availability of the part while waiting for replenishment?