Given the following partial multiple regression ANOVA table, Source 55 clf X1 535.9569 1 X2 1,167.5634 1 X3 18.9886 1 Error 3,459.6803 8 a. [3] How many observations were in the sample? b. [3] What is the total sum of squares and the degrees of freedom for total sum of squares? C. [3] What is the mean squared error? d. [3] Calculate the explained variation. e. [3] Calculate the proportion of the variation explained by the multiple regression model. f. [3] Test the overall usefulness of the model at alpha=0.05. Calculate F and make your decision about whether the model is useful for prediction purposes