Answer:
(A) 
(B) Frequency becomes half.
Step-by-step explanation:
We have been given that the frequency f of vibration of a violin string is inversely proportional to its length L. The constant of proportionality k is positive and depends on the tension and density of the string.
(A) We know that two inversely proportional quantities are in form
, where y is inversely proportional to x and k is constant of proportionality.
Upon substituting our given values, we will get:

Therefore, our required equation would be
.
(B) For part, we have been given that length is twice, so our new frequency will be
and new length
is
.
Upon substituting
in our equation as:




Upon comparing
with
, we can see that
is half the value of
.
Therefore, the frequency of vibration of violin gets half, when we double the length of the string.