A large tank is filled with methane gas at a concentration of 0.690 kg/m3. The valve of a 2.00-m pipe connecting the tank to the atmosphere is inadvertantly left open for 11.0 hours. During this time, 7.40x10-4 kg of methane diffuses out of the tank, leaving the concentration of methane in the tank essentially unchanged. The diffusion constant for methane in air is 2.10x10-5 m2/s. What is the cross-sectional area of the pipe? Assume that the concentration of methane in the atmosphere is zero.