Assume that American lumber companies make 52 billion board-feet of lumber each year, of which 10 billion are exported and 42 billion are sold in the United States. The average price is 30 cents per board-foot. If lumber exports were banned by law, production (now for the domestic market only) would be 48 billion board-feet, and the price would drop to 25 cents per board-foot. How much producer surplus would U.S. lumber producers lose each year as a result of the export ban?