In January of 2018 Bank of America started charging customers a $12 checking account fee. Of course, customers were upset with this change. However, Bank of America claimed that their checking account fees are some of the lowest in the industry. You decide to check Bank of America’s claim and sample 30 random bank customers. A sample of 30 customers paid an average fee of $12.55 per month on their interest-bearing checking accounts. Assume the population standard deviation is $1.75.

a. Construct a 95% confidence interval to estimate the average fee for the population.

b. What is the margin of error for this interval?