An economic forecasting model has been developed for predicting next year's total national retail sales. Of the dozens of economic variables that are known to have an effect on the retail sales, 7 of them ($x_1, x_2, \dots, x_7$) are selected for use in a multiple regression model. Using 113 years' worth of observations on each of the variables and the retail sales, a multiple regression model is fit to the data.
For this model, what are the degrees of freedom (df) for the regression sum of squares, error sum of squares, and total sum of squares?
(a) df for the regression sum of squares:
(b) df for the error sum of squares:
(c) df for the total sum of squares:
