Happy Sunday! I asked you all to answer the question below and you did. Can you tell me why in Step #1 "N" is 30 and not 60? I thought to get the standard error you divide the standard deviation of...

Happy Sunday! I asked you all to answer the question below and you did.  Can you tell me why in Step #1 "N" is 30 and not 60?  I thought to get the standard error you divide the standard deviation of the population/ the square root of the sample size.  Which in this case seems to be 60.  You got the same answer as the book.  I don't understand why you used 30.  Thank you!

The owner of a specialty coffee shop wants to study coffee purchasing habits of customers at her shop. She selects a random sample of 60 customers during a certain week, with the following results:
• The amount spent was X = $7.25, S = $1.75. • Thirty-one customers say they “definitely will” recommend the specialty coffee shop to family and friends.

a. At the 0.05 level of significance, is there evidence that the population mean amount spent was different from $6.50?

d. What is your answer to (a) if the sample mean equals $6.25?