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 $\backslash (\backslash$mathbf$\{3\}\backslash )$ decimal places and final answers to $\backslash (\backslash$mathbf$\{2\}\backslash )$ decimal places.

b$.$ Compute $\backslash (\backslash$pm $2\backslash$mathrm$\{$~s$\}\backslash )$ 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 $\backslash (\backslash$mathbf$\{2\}\backslash )$ decimal places.