This question deals with the physics of resonance and sound. The possible frequency of the pano key is 258hz.
The beat of a frequency is the difference (an absolute value) in the frequencies produced by the two waves.
Beat per second equals |f1 - f2| Where
ft = Frequency of the Tunning fork and
fp= Frequency of the Piano Key
Hence
3 = 261 - fp
Solving for fp,
fp = 261-3
= 258hz
Learn more about Audio Frequencies are:
https://brainly.com/question/27241481