A level physics question

Can someone please explain what I meant to do ?

So, for this question I think you need to know about the proportionality of different quantities in an equation. For example, in the harmonic frequency equation, frequency is inversely proportional to the length of the string, given that other conditions are the same. That’s why they mentioned that tension is the same. Now you know that, you can understand how the frequency changes when the length changes. If you divide the changed length with the original length, you get the scale factor to which the initial length has been ‘shortened down’ to. Using the proportionalities between frequency and length, you should find that you need to divide the initial frequency by the scale factor you calculated earlier to get the new frequency.
Usually, you’d know if it’s a question about equation proportionality when you’re given barely any quantity values, and also told that a value is kept the same.

Also, out of curiosity, what exam board is this?
I’m AQA, and am having my paper 1 physics exam on the 24th 😬

Aqa , and me to and I am so scared for it !