Super built up area

I intend to sell my flat. In the purchase deed of my flat it is mentioned as "Flat measuring an area of 880 square feet or built up area 734 square feet and common area 146 square feet" and in another place mentioned as "Flat containing 734 square feet built up area and 146 square feet on built up common area thus total area of 880 square feet". As the sale value is determined on the Super Built Up Area of the flat also the Stamp Duty for Registration in West Bengal is assessed on the Super Built Up Area only, What is the actual Super Built Up Area of my flat as per the deed? Is it 880 square feet which include 146 square feet of common area or should it be 880 square feet plus 20% making it 1056 square feet. But note that 1056 square feet is nowhere mentioned in my deed. On what Super Built Up Area should my flat be registered when sold?