Could someone double check my math on this?

I have a countertop of 6.97 square meters made of a stone that emits 30.20 Bq of Radon per day and I need to figure out how much the stone adds to the Radon level in the home in pico Curies per liter of air.

30.20 Bq x 27.02 (Bq to pCi conversion factor) = 816.004 pCi x 6.97 sq meters of countertop = 5,687.54 pCi of Radon emitted per day.

12' x 15' kitchen with 8' ceilings would be 12 x 15 x 8 = 1,440 cubic feet -351 cubic feet for cabinets and appliances= 1089 cubic feet of air present.

28.3 liters per cubic foot so 1089 cubic feet x 28.3 = 30,818.7 liters of air present in the room.

5,687.54 pCi of Radon mixed into 30,818.7 liters of air = 0.1845 pCi/liter increase.

Thanks for taking the time.

Al