4. Consider firm j engaged in a monopolistic competitive industry, called j. The demand facing this firm is given as: Qi = S; x [- - b x (P, - P,)] where Of is the quantity demanded facing firm i S is the total sales of industry j, wi is the number of brands in industry j. P; is the price of the product produced by firm i, and P, is the average price in industry j. Also, b is a parameter measuring the price elasticity of demand a. All else being constant, how does an increase in total sales of the industry j affect the demand facing firm ? Provide a real-life (or a made-up) example, justifying your answer. | b. All else being constant, how does an increase in number of brands in industry j affect the demand facing firm ? Provide a real-life (or a made-up) example, justifying your answer. c. All else being constant, how does an increase in average price in industry j affect the demand facing firm ? Provide a real-life (or a made-up) example, justifying your