You can put this solution on YOUR website!
First read this --> http://www.purplemath.com/modules/rtnlroot.htm to see how you can get a list of 'possible real root answers'.
In this case, the answers can be either +-1 or +-5.
Then use 'long division' or synthetic division to test (x+1) (x-1) (x+5)(x-5) to find the one(s) that work.
For me, the quickest way to the answer is to just "plug in" -1, 1, -5 and 5 and see which work. But that won't require using the remainder theorem.