The quarterly sales data (number of copies sold) for a college textbook over the past three years are as follows:

a. Show the four-quarter moving average values for this time series. Plot both the original time series and the moving averages on the same graph.
b. Compute seasonal indexes for the four quarters.
c. When does the textbook publisher experience the largest seasonal index? Does this result appear to be reasonable?Explain.

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Year 2 1800 2900 Year 3 Year 1 1690 940 2625 2500 Quarter 1850 1100 2930 2615