1. [Conceptual] Consider a study investigating the association between retail stores' revenue and their marketing budget. The outcome of interest is store's gross revenue in 2020, yi, for store 2' = 1, . . . ,n. We further observe each store's allocation of marketing budget across three different marketing strategies: strategy A, strategy B, and strategy C. Let Ai be the percent of the ith store's marketing budget spent on strategy A, B; be the percent of the ith store's marketing budget spent on strategy B, and Ci be the percent of the ith store's marketing budget spent on strategy C. These are the only possible ways to spend the marketing budget, so that Az- + Bi + 0%- = 100%. Suppose an analyst ts the following regression model: 112' = 181142' + 5232' + 5302' + 62' (1) (a) Why can we not add an intercept to this model? (b) What diiculties arise in interpreting the estimates of the regression coefcients in this model? (c) How else might you interpret the results of this analysis? (For this model, not results of tting a different model)