Chemistry problem involving ideal gas law?

A series of measurements are made in order to determine mm of unknown gas. First, a large flask is evacuated and found to weigh 134.567 grams. It is then filled with gas to pressure of 735 torres at 31 celcius and reweighed. Its m is now 137.456 grams. Finally, the flask is filled with water at 31 celcius and weighted at 1067.9 grams (density of water at this temperature is .997 grams per mL) uming the ideal gas law applies, calculate the molar mas of the unknown gas