how to solve a,b,c,d part ??

A cell phone provider hires you to determine the number of times per day their customers interact with their smartphone. You take a random sample of 28 customers and find the average number of interactions to be 60 times per day with a sample standard deviation of 6. a. If you are to find a confidence interval for the population mean number of interactions, what distribution would you use and why? . Find a 99% confidence interval estimate for the population mean number of cell phone interactions. . What is the margin of error for the confidence interval you found in part b, and what critical value ( z, or t ) would you use to find d. A representative for the cell phone provider told you they believe the mean number of interactions per day was 65. What would you say to the company representative? Explain