Answer:
T = 708.81 N
Step-by-step explanation:
Given that,
Length of a steel wire in a piano, l =0.54 m
Mass,

We need to find the tension must this wire be stretched so that the fundamental vibration corresponds to middle C, fc = 261.6 Hz
The equation for fundamental frequency is given by :

So, the required tension in the wire is 708.81 N.