(1) Every airline or railroad operating in the state of Montana and selling liquor purchased outside this state for consumption within this state shall pay to the department the excise taxes and state markup that would be applicable to the liquor if purchased from an agency liquor store.
(2) The amount of excise taxes and state markup payable must be determined by multiplying the following factors:
(a) the average liquor used per departure;
(b) the number of departures from Montana on which liquor is served;
(c) the ratio of Montana revenue passenger miles to system revenue passenger miles; and
(d) the applicable excise tax and state markup rates.
(3) From the product, the carrier shall subtract the amount of excise taxes and state markup on purchases of liquor made within this state.