about sample

A firm wants to test the advertising effectiveness of a new television commercial. As part
of the test, the commercial is shown on a 6. 30 PM local news program in Denver, Colorado.
Two days later, a market research firm conducts a telephone survey to obtain information on
recall rates (percentage of viewers who recall seeing the commercial) and impressions of the
commercial.
(a) What is the population for this study?
(b) What is the sample for this study?
(c) Why would a sample be used in this situation? Explain