The owner of the store from Exercise wants to know if the mean age of all customers

Question:

The owner of the store from Exercise wants to know if the mean age of all customers is 25 years old.
a) What is the null hypothesis?
b) Is the alternative one- or two-sided?
c) What is the value of the test statistic?
d) What is the P-value of the test statistic?
e) What do you conclude at alpha = 0.05?