Caroline, a piano tuner, suspects that a piano's A4 key is out of tune. Normally, she would play the key along with her A4 tuning fork and tune the piano to match, but her A4 tuning fork is missing. Instead, she plays the errant key along with her G4 tuning fork (which has a frequency of 392.0 Hz), displays the resulting waveform on a handheld oscilloscope, and measures a beat frequency of 84.6 Hz. Then, she plays the errant key along with her B4 tuning fork (which has a frequency of 493.9 Hz) and measures a beat frequency of 17.3 Hz. What frequency is being played by the out-of-tune key? If the B4 key is supposed to produce a frequency of 493.9, is the frequency of the key lower than it should be ("flat") or higher than it should be ("sharp")?