An aircraft with a Pitot tube mounted on its nose flies at an altitude of 11000 m through still air where the temperature is -56 °C and density is 0.37 kg/m³. a) What is the pressure ratio measured by its Pitot tube when traveling at 68 m/s? b) ... at 240 m/s? c) How much time elapses between the moment the aircraft is above an observer on the ground and the moment the observer hears the aircraft, if the aircraft is flying at 680 m/s?