Two liters of oxygen at 25 degree Celsius and a pressure of 2.3 atm is added to a 3.0 L flask containing nitrogen with a pressure of 3.5 atm at 25...

Two liters of oxygen at 25 degree Celsius and a pressure of 2.3 atm is added to a 3.0 L flask containing nitrogen with a pressure of 3.5 atm at 25 degree Celsius. What is the pressure of the gas mixture.

Are the initial and the final volume the same?