$($a$)$ Using the data in the table above, compute the $3$ months moving average of forecasting from January to December $2019$ and forecast the sales for January $2020$ and February $2020.($b$)$ Given the weights distribution for October $2019(20\%),$ November $2019(30\%),$ December $2019(50\%).$ Please forecast the sales for January $2020,$ using weighted moving average method. $($c$)$ Given $\backslash$alpha $=0\mathrm{.}5,$ please forecast the sales for January $2020,$ using exponential smoothing method.