A cellular telephone company recently conducted research into the length of calls (in minutes) made by customers. In a random sample of 30 calls, the sample mean was 18.6 minutes and the standard deviation was 5.2 minutes.

Construct a 90% confidence interval for true mean call length. Round answer to one decimal place. Enter answer in this form (A, B)

Construct a 99% confidence interval for true mean call length. Round answer to one decimal place. Enter answer in this form (A, B)