25. The following rules apply in establishing if at least 50% of the property of a corporation consists of land at a particular time:(a) such percentage is computed by establishing the ratio between the amounts representing the market value of the land owned by the corporation and the amounts representing the market value of all the property owned by the corporation, after making the deduction provided for in paragraph c;
(b) for the purposes of paragraph a, the land of the corporation includes the land owned by another corporation which is controlled directly or indirectly in any manner whatever by the corporation;
(c) where the market value of the property of the corporation, other than land, is attributable in whole or in part to the market value of land which is included in the land of such corporation in virtue of paragraph b, the market value of the property of the corporation must be reduced by an amount equal to the market value of such land.