The partial pressure of CO2 in the atmosphere

The partial pressure of CO2 in the atmosphere is 3. 9×10-4 atm. When drinking soda is put in a can, assume that there is 2. 0 atm CO2 in the 2. 0 mL gas space above the soda. (The actual CO2 pressure varies with type of soda). What is the approximate ratio of the molar concentrations of CO2(aq) in the soda before it is opened to that in the soda after it has been opened and reached equilibrium with the surrounding atmosphere, i. e. , has “gone flat?”Answer: 5×10^3There is a document for this question, but it has no explanations. Thank you!