Answer:
The population is the population of 3521 people who made credit card purchases.
The sample is the 172 people who returned the survey form.
Step-by-step explanation:
Department mails customers satisfactions forms to those who make credit cards purchase at the store, totaling 3521 people. Thus, the population is the population of 3521 people who made credit card purchases.
Surveys are mailed to 278 of these people, chosen at random, and 172 people return the survey form.
Thus the sample, that is, those from whom the data will be taken and expanded to the rest of the population, is the 172 people who returned the survey form.