K Banking fees have received much attention during the recent economic recession as banks look for ways to recover from the crisis. A sample of 31 customers paid an average fee of $11.82 per month on their interest-bearing checking accounts. Assume the population standard deviation is $1.96. Complete parts a and b below. a. Construct a 90% confidence interval to estimate the average fee for the population. The 90% confidence interval has a lower limit of $ and an upper limit of $ . (Round to the nearest cent as needed.) b. What is the margin of error for this interval? $ (Round to the nearest cent as needed.)