Problems $16$ through $21$ are based on the following data. Observations of the demand

for a certain part stocked at a parts supply depot during the calendar year $2013$ were

Month Demand Month Demand

January $89$ July $223$

February $57$ August $286$

March $144$ September $212$

April $221$ October $275$

May $177$ November $188$

June $280$ December $312$

$17.$ Using a four$-$month moving average, determine the one$-$step$-$ahead forecasts for

July through December $2013.$