Use the moving-average method with n = 3 retrospectively to determine what the forecasts would have been for the last nine months of last year. What are MAD and MSE?

Ben Swanson, owner and manager of Swanson's Department Store, has decided to use statistical forecasting to get a better handle on the demand for his major products. However, Ben now needs to decide which forecasting method is most appropriate for each category of product. One category is major household appliances, such as washing machines, which have a relatively stable sales level. Monthly sales of washing machines last year are shown below