A retailer sells christmas tree during the christmas time where the sales history is provided in column A and B$.$ The reiler buys the trees from a supplier by $$20/$unit and then sell them to the market by $$25/$unit$.$ The retailer can also return leftovers at the end of the season and the suppliers pays back $$10/$unit$.1.$ Forecast the demand for $2021$ by using any technique $(0\mathrm{.}5$ point$),$ and calculate the standard devision of the demand $(1$ point$)$ by using the sales history. $2.$ Used the results of part $1$ to calculate the optimum order quantity from the supplier $(1\mathrm{.}5$ point$).$