Please solve the following questions (18-23) by:

1. stating the null and alternative hypothesis,
2. choose the test (Z or t),
3. identify the level of significance and corresponding critical value
4. calculate Z or t
5. determine if your results are significant (reject, fail to reject)
6. State your conclusion
7. find, present, and interpret the p-value

1. The mean lifetime for all cardiac stents is 8.9 years. A medical device company has implemented some improvements in the manufacturing process and hypothesizes that the lifetime is now longer in their stints. A study of 40 new devices reveals an average lifetime of 9.7 years with an unknown standard deviation of 3.4 years. Is there statistical evidence of a prolonged lifetime of the stents? Run the test at =.05.