The file P14_29.xlsx contains monthly time series data for total U.S. retail sales of building materials (which includes retail sales of building materials, hardware and garden supply stores, and mobile home dealers).

a. Is seasonality present in these data? If so, characterize the seasonality pattern.

b. Use Winters’ method to forecast this series with smoothing constants α = β = 0.1 and γ = 0.3.

Does the forecast series seem to track the seasonal pattern well? What are your forecasts for the next 12 months?