A drill sergeant standing just inside a bunker doorway that is 0.951 m wide blows a whistle to summon the cadets from the exercise yard. Everyone responds except for Eli, who was about 90 m away from the bunker, at an angle of 17.9 degrees from a line normal to the doorway. Eli claims that he did not hear the whistle because he was standing at the second-order diffraction minimum for the sound waves. What whistle frequency is consistent with his explanation? The speed of sound is 343 m/s at this temperature. If you get this problem wrong, drop and give us 50.0 pushups!