Please also include the excel sheet (with formulas), so I can see how it was done.

The data in the spreadsheet that follows refer to a quarterly series that is purely seasonal, as in Section 4.2. The values for year 1 are used as starting values (forecasts) for year 2 Use the purely seasonal version of exponential smoothing with y-0.5 to generate fore- casts for year 3 Data 50 30 20 Year Forecasts Quarter 35 15 80 50 30 20 4 4