Please help me..

The Great Northwest Outdoor Company is a catalogue sales operation that specializes in outdoor recreational clothing. Demand for its items is very seasonal, peaking during the holiday season and during the spring. It has accumulated the following data for order per "season" (quarter) during the past five years: a. 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 2011). b. Develop a separate linear trend line forecast for each of the four seasons and forecast each season for year 6. c. Which of the two approaches used in parts (a) and (b) appear to be the most accurate? Use MAD to verify your selection