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

$\backslash$table$[[$Year$,,1,2,3,4,5,6,7,8,9],[$Sales $(000)$:$,38\mathrm{.}40,44\mathrm{.}50,48\mathrm{.}00,53\mathrm{.}40,56\mathrm{.}20,57\mathrm{.}10,62\mathrm{.}80,68\mathrm{.}10,74\mathrm{.}80,]]$

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a$.$ Using an appropriate model, forecast textbook sales f$$r each of the next five years. $($Round your intermediate calculations to $3$ decimal places and final answers to $2$ decimal places.$)$

$\backslash$table$[[$Year$,10,11,12,13,14],[$Forecast$,,,,,]]$

b$.$ Compute $\frac{+}{-}2s$ control limits for the control chart for forecast errors using just data from the original nine periods. $($Round your intermediate calculations to $4$ decimal places and final answer to $2$ decimal places.$)$

Control limits are

$0+-$

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

$\backslash$table$[[$Year$,10,11,12,13,14],[$Sales $(000)$:$,78\mathrm{.}40,82\mathrm{.}00,87\mathrm{.}00,92\mathrm{.}10,96\mathrm{.}60]]$

Is the forecast performing adequately?