Many U.S. consumers are using debit cards to avoid accruing debt (creditkarma.com, July 27, 2019). Based on a sample of 100 U.S. consumers, a researcher finds that the average amount spent annually on a debit card is $7,790. Assume that the population standard deviation is $500.

a. At 99% confidence, what is the margin of error?

b. Construct the 99% confidence interval for the population mean amount spent annually on a debit card.