The cost for Tamiflu this flu season is normally distributed with a mean of $162 with a standard deviation of $12. A random sample of 18 pharmacies is selected and the price of Tamiflu is recorded. a.) Determine the mean of the sample means of the cost of Tamiflu at the 18 randomly selected pharmacies. Use correct mathematical notation. b.) Determine the standard error of the sample means of the cost of Tamiflu at the 18 selected pharmacies. Use correct mathematical notation. c.) Calculate the probability that a random sample of 18 pharmacies has an average cost of less than $157 for Tamiflu.