Radon-222 decays to Polonium-218, which further decays to a stable nuclide. The half-lives are T1/2(Rn)=3.8d and T1/2(Po)=3.1min, respectively. Initially only Radon-222 is present. Compute, correct to two significant figures, the time (in minutes) after which the activity of Polonium-218 becomes equal to that of Radon-222.