density is defined as mass/volume, therefore
mass = volume/density
The density is given in kg/m3
The volume needs to me in m3 for the units to mesh. The answer will be in kg and need to be converted to grams.
You can convert all the ft to meters: 10ft (1m/3.28 ft), for example
Find the volume by multiplying the dimensions of the room together and get volume in m3.
Take care and please consider a tutor.