please answer c and d

Currently patrons at the library speak at an average of 70 decibels. Will this average decline after the installation of a new computer plug in station? After the plug in station was built, the librarian randomly recorded 54 people speaking at the library. Their average decibel level was 67.4 and their standard deviation was 6. What can be concluded at the the a = 0.05 level of significance? a. For this study, we should use t-test for a population mean b. The null and alternative hypotheses would be: HO: HYVE 70 H1 : HV V