Physics - Density please help me?

The density of air at standard atmospheric pressure and 15�C is 1.23 kg/m3. (a) What is the total m of the air in a rectangular room that measures 5.25 m � 4.20 m � 2.15 m? (b) What is the weight of the air in the room? (c) What is the weight of the air in the Pentagon office building in Washington, DC, which has a volume of 2.2�10^6 m3?