Data:

Quarterly Glass Container Demand

Year	First Qtr.	Second Qtr.	Third Qtr.	Fourth Qtr.
1990	17,446.	17,748.	18,971.	17,802.
1991	17,595.	19,360.	19,413.	18,315.
1992	17,785.	18,338.	19140.	18,083.

Question:

Quarterly sales (in thousands of units) of a product over the last two years have been 26, 29, 30, 27, 28, 32, 33, and 30. Plot the data and forecast for the next period using Winters Seasonal Model.

Now, assume sales for the ninth quarter turned out to be 32. Update your parameter estimates and forecast sales for period 10.