Answer:
f = 22
Explanation:
From the question

Meaning, f is inversely proportional to √g
Therefore,

Where, k is constant
Making k subject of the formula,
k = f·√g
Slotting our values of f = 10, when g = 121,
k = 10·√121
k = 10·11
k = 110
Now that we have our constant,
To find f when g = 25,

Slotting in,
k = 110, g= 25,
We have,
f = 110/√25
f = 110/5
f = 22, when g=25