Problem $18-4($Algo$)$

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

$\backslash$table$[[,,],[$January$,$LAST YEAR,THIS YEAR$],[$February$,325,315],[$March$,432,335],[$April$,455,340],[$May$,495,445],[$June$,440,415],[$July$,475,385],[$August$,390,355],[$September$,330,285],[$October$,350,350],[$November$,490,],[$December$,580,],[,495,]]$

Develop a forecast for the fourth quarter using a three$-$quarter, weighted moving average. Weight the most recent quarter $0\mathrm{.}50,$ the second most recent $0\mathrm{.}25,$ and the third $0\mathrm{.}25.$ Do the problem using quarters as opposed to forecasting separate months.

Note: Round your answer to $2$ decimal places.

Answer is complete but not entirely correct.

Forecast for the fourth quarter

$673\mathrm{.}75$