The company's marketing department models the demand function as Q = a + bP + cM + dP_S, where Qis the annual demand for your product measured in thousands of units, Pis the price of the headphones, M is the average annual family income measured in thousands of dollars, andP_S is the price of the stereos with the technical specifications needed to have an excellent listening experience. The output given by Excel after running the corresponding OLS regression is the following:

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