What is the square root of 64 over 225 with a negative outside of the radical?

The square root of  (64/225)  is the same as  √64 / √225 . 
That could make the whole thing easier.

Do you know what either of those separate square roots is ?

You're right !    I'm so impressed!
The square root of  64  IS  8, and the square root of  225 surely is  15 .
You really know your stuff !

So now, the expression is  √64 / √225  =  8 / 15 .

Oh, I almost forgot, it has a negative sign before it.  OK,so the answer is - 8/15 .

r   = 2.65m

good luck!

cutie~