An airplane pilot is about to leave a long cross-country trip that will require him to use oxygen. He's noticed that the amount of oxygen in the bottle in the plane is low, so he must refill it from the large supply tank of oxygen in his hanger. The large supply tank is at a pressure of 50 MPa. The small bottle has a volume of 0.3 m3 and is connected to the supply tank by a hose that is 10 mm in diameter. The temperature of the oxygen remains constant in both tanks at 15 degrees C. The mass flow rate into the small bottle is m' = 0.1 (pt-p) A/sqrt(RT) where pt = 50 MPa, p is the pressure in the small bottle, A is the cross-sectional area of the hose, R is the gas constant for oxygen, and T is the temperature. If the desired final pressure in the small tank is 20 MPa and it takes 35 seconds to fill it, what is its initial pressure?