(b) Payment of agreed tax. The executor shall pay to the commissioner of taxation and finance the amount of tax fixed in the agreement described in subsection (a) of this section. In the event the aggregate amount payable under such agreement to the states involved is less than the maximum credit allowable to the estate against the United States estate tax imposed with respect thereto, the executor forthwith shall also pay to the commissioner of taxation and finance so much of the difference between such aggregate amount and the amount of such credit, as the amount payable to the commissioner under the agreement bears to such aggregate amount.
(c) Definition. As used in this section the word "state" means any state, territory, or possession of the United States, the District of Columbia and the Dominion of Canada or any province thereof.