There are six white-collar workers at a university department with the following ages:

56, 38, 29, 58, 43, 47
Two of the workers are to be chosen at random.
a. How many possible samples of two workers are there?
b. List all possible samples.
c. Find the probability function of the sampling distribution of the sample means.
d. Verify directly that the mean of the sampling distribution of the sample means is equal to the population mean.