Use two month moving average and use trend projection method to forecast the coal sales. Based on the analysis in part $($a$)$ and $($b$),$ which method moving average trend projection provides the better forecast? Explain. $(c)$ Then, use the least squares regression method $to$ drive a forecasting equation.. $(d)$ Lastly, what are the stimated coal sales $if$ the severity $of$ weather index $is9.$ Weather Index $=X,$ Coal Sales $=Y$

X Y

$12$

$33$

$42\mathrm{.}5$

$22$

$12$

$73\mathrm{.}5$