According to the U. S. National Weather Service, at any given moment of any day, approximately 2000 thunderstorms are occurring worldwide. Many of these storms include lightning strikes. Sensitive electronic equipment is used to record the number of lightning strikes worldwide every day. 14 days were selected at random, and the number of lightning strikes on each day was recorded. The sample mean was 8.7 million. Assume the distribution of the number of lightning strikes per day is normal and has a population standard deviation of 0.47 million. Please use 4 decimal places for all critical values. (1 pt.) a) What assumptions are required so that you can construct a confidence interval for the mean number of lightning strikes per day?