The original question got deleted somehow; here it is again for reference:
"How many grams of methoxyflurane (C3H4Cl2F2O) must be present in a 49.0 L tank of compressed air with a pressure of 100. atm at 25.0°C in order for 1.2 mm Hg pressure of methoxyflurane to be present in the lungs of a patient at 1.00 atm?"