Quick physical chemistry question

[gman5]

Calculate the final temperature of a sample of carbon dioxide of mass 16.0g that is
expanded reversibly and adiabatically from 500mL at 298,15K to 2.00L.

I know the answer and understand how to do the problem except for 1 part.

The equation to get the solution is : Tf = Ti (Vi/Vf)^(1/c)

The part I cannot figure out is how to find c. I know c = Cv,m/R = 3.463, but when I try to calculate c I get something other than 3.463.

 

[gman5]

nevermind, it turns out that some information needed to make the calculation is contained in the back of the book, so I figured it out.