$(16\%)$ A simple forecasting method for weekly sales of SSD drives used by a local

computer dealer is to form the average of the two most recent sales figures. Suppose

sales for the drives for the past $12$ weeks were

Week $123456789101112$

Sales $8957144221177280223286212275188312$

a$.$ Determine the forecasts for week $13$ using $3-,6-$ and $12-$ week moving average.

b$.$ Using $3-$week moving average to forecast the sales for week $7$ to $12.$

c$.$ Compute the MAD for b$.$

d$.$ Using $6-$week moving average to forecast the sales for week $7$ to $12.$ What effect

does increasing N from $3$ to $6$ have on the forecast?