SUPER BUILT UP AREA OF MY FLAT

My flat is in Kolkata purchased in 1992 when the Super Built Up Area was not mentioned in the purchase deed. Now as the sale price and stamp duty both are calculated on the Super Built Up Area I need to know the same for 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 from the recitations mentioned in the Purchase Deed as quoted hereinabove should the Super Built Up Area of my flat be taken as 880 square feet or should it be 880 square feet plus 20% = 1056 square feet. Please note 1056 square feet is nowhere mentioned in the said Purchase Deed. What should be the Actual SUPER BUILT UP AREA for my flat as per the Purchase Deed. Expecting your kind co-operation. Awaiting your valued guidance in this regard.