Omputer Action Company sells computers and computer parts by mail. The company assures its customers that products are mailed as soon as possible after an order is placed with the company. The distribution of the times taken to mail products is known to follow a normal distribution. A sample of 28 recent orders showed that mean time taken to mail products for these orders was 70 hours and the standard deviation was 14 hours. If you were asked to find a 95% confidence interval for the mean time taken to mail products for all orders received at the office of this company, would you use z or t?