9. (20 pts) A simple random sample of 30 cell phone batteries resulted in a mean life span of 4.7 years with a standard deviation of 0.95 years. Use a 0.05 significance level to test a claim that the mean life span of cell phone batteries is equal to 5 years. [Note: Assume the population standard deviation is unknown.] a. Clearly identify and state the null hypothesis He and the alternative hypothesis H. b. Determine the critical value(s) and the value of the appropriate rest statistic (to nearest 0.001). [Note: Table A-3 might be helpful for critical value(s).] c. Do you reject or fail to reject the null hypothesis? Justify your answer. d. Using Figure 8-5 on p. 366, clearly state your final conclusion