A. For the purpose of taxation, any railway car owned by an organization and used exclusively within this state or used partially within and partially without this state has situs within this state.
B. The term "gross earnings" shall be construed to mean all earnings on business beginning and ending within this state and on a proportion, based on the division of mileage in this state by the entire mileage over which business is done, of all interstate business passing through, into or out of this state.