Super Cruiseline offers nightly dinner cruises departing from several cities on the East Coast of the United States including Charleston, Baltimore, and Alexandria. Dinner cruise tickets sell for $80 per passenger. Super Cruiseline's variable cost of providing the dinner is $40 per passenger, and the fixed cost of operating the vessels (depreciation, salaries, docking fees, and other expenses) is $240,000 per month. The company's relevant range extends to 18,000 monthly passengers. If Super Cruiseline sells an additional 600 tickets, by what amount will its operating income increase (or operating loss decrease)? First, identify the formula, then compute the operating income increase (or operating loss decrease)