It works out at 4.37 mg of carbon monoxide based on the room dimensions.
The concentration is 48
You have the dimensions of the room in feet, so the simplest way is probably to convert these into metres, and then work out the volume in cubic metres.
1 foot is 0.3048 m, so the dimensions are:
10.6 feet = 10.6 x 0.3048 = 3.23 m
14.8 feet = 14.8 x 0.3048 = 4.51 m
20.5 feet = 20.5 x 0.3048 = 6.25 m
Now you can work out the volume of the room:
3.23 x 4.51 x 6.25 = 91.046 cubic metres.
Now you can work out the mass of carbon monoxide by multiplying the concentration by the volume.