1. A manufacturer wants to increase the shelf life of a line of cake raises. Past records indicate that the average shelf life of the mix is 215 days. After a revised mix has been developed, a sample of nine boxes of cake mix gave these shelf lives (in days}: 215, 21?, 21s, 21s, 21s, 21?, 212, 21s, and 213. Using a = 11.1125, has the shelf life of the cake mix increased? What is the computed t and critical t values