a$-2.$ Forecast the preceding eight years, and determine the forecast errors. $($Negative answers should be

indicated by a minus sign. Do not round intermediate calculations and round your final answer to $2$

decimal places.$)$

Year Sales$(000)$ Forecast Error Error$\backslash$Lambda $2$

$137\mathrm{.}60$

$242\mathrm{.}40$

$349\mathrm{.}30$

$453\mathrm{.}40$

$555\mathrm{.}20$

$657\mathrm{.}70$

$760\mathrm{.}80$

$869\mathrm{.}20$

a$-3.$ Construct $2$s control limits$.($Round the final answer to $2$ decimal places.$)$

$2$s control limits are $\backslash$pm

b$.$ Using the model, forecast textbook sales for each of the next five years. $($Round the final answers to $1$