Suppose that roxy's marginal cost of a jacket is a constant $200. 00 and the total fixed cost at one of its stores is $2,100 a day. This store sells 30 jackets a day, which is its profit-maximizing number of jackets. Then the stores nearby start to advertise their jackets. The roxy store now spends $1,500 a day advertising its jackets, and its profit-maximizing number of jackets sold jumps to 60 a day.