Seal$-$Fine Sash Company has three years' quarterly demand data for its standard bedroom window unit. The production control manager uses the following data for demand forecasting:Number of Window UnitsThree Years AgoTwo Years AgoLast YearWinter$190215401$Spring$147210510$Summer$494755925$Fall$7731,0881,482$a$.$ Calculate the three$-$quarter moving average forecast. To what future time period does this moving average apply?b$.$ Which of the following moving average time spans is better, three quarters or four quarters? Prove your answer by calculating mean absolute deviations $($MADs$)$ using all $12$ quarters of data. $($If suitable computer facilities and software are available, process the