Develop a seasonally adjusted forecast model for these order data. Forecast demand for each quarter for year $6($using a linear trend line forecast estimate for orders in year $6).$

a$.$ Develop a separate linear trend line forecast for each of the four seasons and forecast each season for year $6.$

b$.$ Which of the two approaches used in $($a$)$ and $($b$)$ appears to be the more accurate? Use MAD to verify your selection.