As in Exercise 2.21, a sequence of seven people walk into a post office and only their

Question:

As in Exercise 2.21, a sequence of seven people walk into a post office and only their sexes are noted. Assume that each of the seven customers is equally likely to be a man or a woman. Let X denote the number of customers that are female.
a. Find the mass of X.
b. Find the CDF of X.