In an experiment, argon is allowed to effuse through a tiny opening into an evacuated 5.00 x 10^2 mL flask for 30.0 seconds, at which point the pressure in the flask is found to be 15.0 mm Hg. The experiment is repeated using unknown gas at the same temperature and pressure. After 30.0 seconds, the pressure is found to be 47.4 mm Hg. What is the molar mass of the gas?