Refer to the data in the file that accompanies this book named COGS.xlsx representing monthly cost of goods sold data for a retail store.

Use regression analysis to fit an additive seasonal model with linear trend to the data set.

a. What is the estimated regression function?
b. Interpret the R² value for your model.
c. Interpret the parameter estimates corresponding to the indicator variables in your model.
d. Prepare a line graph comparing the linear trend predictions against the original data.
e. What are the forecasts for each of the next 6 months using this technique?