A textbook publishing company has compiled data on total annual sales of its business texts for the preceding nine years:

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a$.$ Using an appropriate model, forecast textbook sales for each of the next five years.

Note: Round your intermediate calculations to $3$ decimal places and final answers to $2$ decimal places.

b$.$ Compute $+-2s$ control limits for the control chart for forecast errors using just data from the original nine periods.

Note: Round your intermediate calculations to $4$ decimal places and final answer to $2$ decimal places.

Control limits are

c$.$ Suppose actual sales for the next five years turn out as follows:

Is the forecast performing adequately?

Yes

No