You have been assigned to analyze automobile manufacturers and as a first step in your analysis, you decide to model monthly sales of lightweight vehicles to determine sales growth in that part of the industry. Figure 2 gives lightweight vehicle monthly sales (annualized) from January 1992 to December 2000.
FIGURE 2 Lightweight Vehicle Sales

Monthly sales in the lightweight vehicle sector, Sales t, have been increasing over time, but you suspect that the growth rate of monthly sales is relatively constant. Write the simplest time-series model for Sales t that is consistent with your perception.

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20 19 18 17 16 wwzmammoy 15 14 13 12 П mтITIT ITTT ITИ 1992 1993 1994 1995 1996 1997 1998 1999 2000 Year Millions of Units (Annualized)