On a particular day Citizens Advice, a consumer-advice bureau in London, received 215 calls. For a random sample of 49 of these calls, it was found that the mean time taken in providing the requested advice was 8.42 minutes, and the sample standard deviation was 5.86 minutes.
a. Find a 90% confidence interval the mean time taken per call.
b. Find a 99% confidence interval for the total amount of time taken in answering these 215 calls.