What does the air in the living room of a man weigh if its dimensions are 3.2m,4.8m and a height of 3.5m respectively, When the air density is 1.21kg m at1.0at m and g = 10.0ms

Just recall your basic formulas:

volume = length*width*height
mass = volume * density
weight = mg
Now just plug in your numbers

oh, and
g is m/s^2, not ms
density is kg/m^3, not kg m