math

The square roots have indentical indices. So, one may take the square root of 300 (the product of 60 and 5) . The answer can be rounded to 17.32.

MEGUSTAMILK's answer is good if you just want an estimate.
This is how you simplify
root5 * root60
=root 300 (just as megustamilk said)
Next you have to look for a square number that goes into 300, if there isn't one then you would not be able to simplify any more.
But 100 goes into 300 and it is a square number

root 300 = root(100*3) = root100 * root3 = 10root3