If demand in the United States is given by Q1 = 7,200 - 300p1, where p1 is the price in the United States, and if the demand in England is given by Q2 = 3,600 - 200p2, where p2 is the price in England. There is no cost to produce this commodity, if the firm is profit maximizer, then the difference between the price charged in England and the price charged in the United States will be?