You purchase a house with a known radon problem. The house has a dirt-floor crawl space (1m high). The emission rate of radon into the crawl space is reported to be 0.6 pCi/m^2-s. An exhaust system was added to provide 1 air exchange per hour (ACH) in the crawl space. The outdoor concentration of radon is 1 pCi/L. Estimate the radon concentration in the crawl spce (in pCi/L). Briefly describe why you need to assume that the air in the crawl space is completely mixed.