B. Mixed beverage carrier licensees may obtain from other lawful sources alcoholic beverages to be sold as mixed beverages on trains, boats or airplanes of the licensees provided there is paid to the Board in lieu of the taxes otherwise directly imposed under this chapter and any markup otherwise charged by the Board, a tax of ten cents for each of the average number of drinks of mixed beverages determined by the Board as having been consumed within the geographical confines of the Commonwealth on such trains, boats or airplanes. Such tax shall be calculated on the basis of the proportionate number of revenue passenger miles traveled within the Commonwealth by such a licensee in relation to the total quantity of all alcoholic beverages obtained either inside or outside the Commonwealth by the licensee for consumption on trains, boats or airplanes of the licensee. Such tax shall be paid to the Board on a quarterly basis.