Question

At normal temperature and pressure, air has

Answer 1

The density of any material can be calculated using the following rule:
density = mass / volume
Therefore,
mass = density x volume

Density of air is 0.001184 g/mL. To convert it to  kg/m^3, multiply by 1000. 
Density of air = 0.001184 g/mL x 1000 = 1.184 kg/m^3

Now, let's calculate the volume of air. The volume of air will be exactly equal to the volume of the room that the air occupies.
volume of air = volume of room = length x width x height
volume of air = 4 x 2.38 x 3.77 = 35.8904 m^3

Finally, we will substitute in the previously mentioned rule to calculate the mass as follows:
mass = density x volume = 1.184 x 35.8904 = 42.494 kg.