sure
the ideal gas law is as follows:
PV = nRT, where P = pressure, V = volume, n = number of moles of gas, R is a gas constant, and T is temperature in Kelvin.
given variables: V = 6 liters, n can be calculated from the grams of co2 given (mw of co2 is 44g/mol, so 300g of co2 is 6.82 moles), R comes from a database, it can change depending on what units you are working with, so be mindful, in this case will be 8.31e-2 Lbar/Kmol, and temperature is in Kelvin. and of course you are solving for p.
so P(6L) = (6.82mol)(8.31e-2Lbar/Kmol)(373K)
solve the equation to yield 35.2 bar
hows that sit?