The data file Quarterly Sales shows quarterly sales of a corporation over a period of 6 years. Use the Holt-Winters seasonal method to obtain forecasts of sales up to eight quarters ahead. Employ...

The data file
Quarterly Sales
shows quarterly sales of a corporation over a period of 6 years. Use the Holt-Winters seasonal method to obtain forecasts of sales up to eight quarters ahead. Employ smoothing constants a = 0.5, b = 0.6, and g = 0.7. Graph the data and the forecasts.