Answer:
Part a)

Part B)
percentage increase is
%
Explanation:
Part a)
As we know that the beat frequency is

after increasing the tension the beat frequency is decreased and hence the tension in string B will increase
So we have


Part B)
percentage increase in the tension of the string will be given as


now we have

so we have


so we have

percentage increase is

The answer is the letter "C" ( I have honors science I am good at this type of stuff )
Hope I helped :) ( ask me for help when u need it :)
Earths atmosphere, Temperature, Plant life and Oxygen I guess