The following data report total, monthly, U.S. new car sales in millions of dollars from January 2019 to December 2021. (To find the data, go to https://www.census.gov/retail/index.html#mrts, find “Monthly Retail Trade Report,” then select “Time Series/Trend Charts.”)

a. Graph the data.b. Based on the graph, describe the time series pattern.c. For this time series, why is forecasting with a seasonally adjusted trend model appropriate?d. What is the average monthly trend in new car sales?e. Evaluate a seasonally adjusted trend forecasting model. What are the MAD and MAPE?f. What are the monthly seasonal indexes? When are new car sales the highest? When are new car sales the lowest?g. Forecast new car sales with error for the next 9 months.h. In your judgment, are the forecasts “good”? What disclaimer would you include with your forecast?

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Month January February March April May June July August September October November December 2019 $67,012 67,456 82,564 76,907 83,937 78,207 82,550 88,148 76,300 79,728 78,776 82,739 Year 2020 $72,074 74,360 59,487 50,131 77,773 81,593 84,691 86,015 85,909 87,522 79,269 92,388 2021 $79,954 77,194 107,329 105,362 105,868 100,052 98,633 93,126 89,210 90,324 88,409 95,849