It would have been possible to answer the question if there was any information on what units were used for 15 x 21. There is no way to tell whether that was feet, yards, metres or some historic measure like a cubit!
270 Square Feet.
208 square feet.
143.3 square feet.
139.75 square feet
154 square feet.
182 square feet.
200 square feet.
201.6 square feet.
270 Square Feet.
144 square feet.
126 square feet
31.4167 square feet.
56 SQUARE FEET
200 square feet
A room that is 12 feet by 13 feet is 156 square feet in area
About 288.17 square feet.
208 square feet.