I have to solve the below mentioned question (a-c) for an online class until tonight 7pm. Can anyone please kindly help me with this? I am really stuck with this and another question.

Thank you so much!

A manufacturer wants to increase the shelf life of a line of cake mixes. Past records indicate that the average shelf life of the mix is 216 days. After a revised mix has been developed, a sample of nine boxes of cake mix gave these shelf lives (in days): 215, 217, 218, 219, 216, 217, 217, 218 and 218. At the 2.5% significance level, the manufacturer wants to test if the shelf life of the cake mix increased.
a What is the null and alternative hypotheses of the test?

b Determine the decision rule for the test.

c What is the manufacturer’s conclusion about the shelf life of the cake mix?