217.12. For the purposes of the definition of “qualifying fiscal period” in the first paragraph of section 217.10 and subparagraph i of paragraphs b and c of section 217.15, a particular business of a taxpayer is deemed to include another business substituted therefor, or for which the particular business was substituted, where(a) all or substantially all of the gross revenue of the particular business is derived from the sale, leasing, rental or development of properties or the rendering of services; and
(b) all or substantially all of the gross revenue of the other business is derived from the sale, leasing, rental or development, as the case may be, of properties similar to those contemplated in paragraph a or the rendering of services similar to those contemplated in paragraph a.