Suppose SSR(X1) = 9140 and SSR(X2) = 2177. Under what condition can you calculate SSR(X1, X2)? What would be the value? [Hint: Look at Example 1 on Pastry Sweetness in Section 5.5 Further Examples and pay particular attention to point number 2 about R2. What does it say about the sums of squares if the SLR R2 values sum to the MLR R2 value? And what is special about the predictors in this example?]