I can't remember right off what the units should be in this formula.
Vrms = sqrt(3RT/M)
R = gas constant
T = temperature
M = mass of molecule (CO2 in this case)
As you see it is an easy plug and chug with the right units, but I do not remember which gas constant to use, but temperature should be in Kelvin as all the gas constants use Kelvin. They all contain mol also, so that M might need to be mol.
You should be more familiar than I with what units are needed here as it has been too many years since I did one of these problems.