In the formula in the first paragraph,(a) A is the aggregate of the amounts payable by the specified person under this Part for the specified person’s taxation year in which the trust’s year ends;
(b) B is the amount that would be determined in accordance with subparagraph a if the aggregate of the amounts payable by the specified person under this Part for the specified person’s taxation year in which the trust’s year ends were computed without reference to the contribution; and
(c) C is the amount recovered before the particular time from the specified person, and any other joint contributor in respect of the trust and the contribution, in connection with the liability of the specified person in respect of the contribution.