Great Cruiseline offers nightly dinner cruises off the coast of Miami, San Francisco, and Seattle. Dinner cruise tickets sell for $60 per passenger. Great Cruiseline's variable cost of providing the dinner is $30 per passenger, and the fixed cost of operating the vessels (depreciation, salaries, docking fees, and other expenses) is $270, 000 per month. The company's relevant range extends to 14, 000 monthly passengers. Use this information to compute the following: if Great 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)