R.I. Gen. Laws § 39-17-4
In case any corporation shall do business in more than one town or city, and it shall be unable to ascertain the amount of its gross earnings in each town or city separately from actual accounts kept thereof, its returns of gross earnings to be made as provided in § 39-17-3 shall state the gross earnings of its entire business and the length of its wires, pipes, mains, or tracks in the streets and highways of each town or city, and the gross earnings from its business in the town or city shall be taken to be that proportion of the whole gross earnings that the length of its wires, pipes, mains, or tracks in the streets and highways of the city or town bears to the total length of all its wires, pipes, mains, or tracks in streets and highways.
R.I. Gen. Laws § 39-17-4