For the purposes of this formula,(1) A is the lesser of(a) an amount equal to the tax calculated on the fair market value of the immovable at that time; and
(b) an amount equal to the total of the tax that was or would, but for sections 75 and 80, have been payable by the registrant in respect of the acquisition of the immovable and the tax that was payable by the registrant in respect of improvements to the immovable or, where the registrant was deemed under section 264 to have received a supply of the immovable at an earlier time, the total of the tax deemed under that section to have been paid by the registrant at that earlier time and the tax that was payable by the registrant after that earlier time in respect of improvements to the immovable;
(2) B is the percentage that, immediately before that supply, the use of the immovable in commercial activities of the registrant is of the total use of the immovable;
(3) C is the percentage that, immediately after that time, the use of the immovable in commercial activities of the registrant is of the total use of the immovable; and
(4) D is the tax, if any, that the registrant is deemed under section 221 to have collected at that time in respect of the immovable.