The Super Bowl is a big viewing event watched by close to 200 million Americans that is also a big event for advertisers. The file Super Bowl Ads Costs contains the average cost for 30-second ads that ran between the opening kickoff and the final whistle for the 2004 to 2019 Super Bowls.

a. Construct a time-series plot.
b. What pattern, if any, is present in the average cost for 30-second ads that ran between the opening kickoff and the final whistle?