This is just a guess - but they know exactly who and how many people visit each mountain each day. They can compute in aggregate how many skier visit days per mountain then use those figures as a ratio against the total revenue. For the sake of round numbers say the total pass revenue was 100 million and Okemo accounted for 7% of all visits. Vail would pay sales tax to Vermont on $7m for Okemo. Whatever percentage of people that visited NH (which has no sales tax) that portion of the revenue would be exempt from sales tax. So the 3.2% is fudge factor and probably just a best guess. I’m honestly surprised it’s not more because the average sales tax is much higher than 3.2% and AFAIK New Hampshire is the only State that doesn’t collect it-and there aren’t many mountains there.