Here are the data for the past $21$ months for actual sales of a particular product:

Table Summary: A table with three columns. The first column lists the months. The second column is last year, and the third is this year.

Last Year This Year

January $300275$

February $400475$

March $425350$

April $450425$

May $400400$

June $460350$

July $400350$

August $300275$

September $375350$

October $500$

November $550$

December $500$

The fourth quarter using a three$-$quarter, weighted moving average. Weight the most recent quarter $0\mathrm{.}5,$ the second most recent $0\mathrm{.}25,$ and the third $0\mathrm{.}25.$ Do the problem using quarters as opposed to forecasting separate months.