The formula for the frequency in a stringed instrument : \(f = \frac{1}{2} \sqrt{\frac{T}{m}}\)
f = frequency; T = tension in the string; m = mass per unit lenth of the string.
f\(_1\) = 14 = \(\frac{1}{2} \sqrt{\frac{T}{m}}\).
When T is quadrupled, we have
f\(_2\) = new frequency = \(\frac{1}{2} \sqrt{\frac{4T}{m}}\)
= 2(\(\frac{1}{2} \sqrt{\frac{T}{m}}\))
= 2 f\(_1\)
= 2 x 14
= 28 Hz