A 15m x 15m x 3.0m basement had a high radon content. On the day the basement was sealed off from its surroundings so that no exchange of air could take place, the partial pressure of222Rn was 1.2*10-6 mmHg. Calculate the number of 222Rn isotopes (t1/2= 3.8d) at the beginning and end of 34 days. Assume STP.