You firat do the calculation 6,000+9*11 then you subtract 3,500 because the seasonal variations must all total in 0. You had seasonal variations of +4,500 +2,000 -3,000. So you needed -3,500 in order to achieve the forecast sales.
I figured that each box ticket cost $600 and not that the whole batch of 10 tickets has a cost of $600. Why did you assume that part, when all the other numbers in that table were supposed to be selling price/ticket and variable cost/ticket sold? Maybe i missed some information provided, reading about your answer I’m not so sure, maybe i missed information provided in the scenario.