Answer:
5√7
Explanation:
What we want to do is first just put the 175 in a sqrt like this:
√175
Next we do prime factorisation to try and simplify further.
 175
 / \
 25 7
 / \ 
5 5
We can figure out that this out √5^2 times 7
we can cancel the sqrt and the squared and simplify to 5√7
So there is your answer, 5√7. 
 
If you have any questions feel free to ask. Also for the prime factorisation the formatting may be off, sorry for the inconvenience and have a good day!