Based on a random sample of 30 U.S. workers, a researcher found that the average (X) number of vacation days a U.S. worker takes per year is 16. The sample standard deviation (s) is 12 days.

The goal is to construct a 99% confidence interval for the average () number of vacation days taken by U.S. workers per year. Assume that the number vacation days taken by U.S. workers is normally distributed.

1. The critical value (CV) needed for 99% confidence interval estimation is

Select one:

a. 2.76

b. 2.46

c. 2.33

d. 2.58

PLEASE EXPLAIN.