If you do a factor tree (I did it on paper), you will find that 140 can be expressed as 2*2*5*7. Since we have two twos, we can factor them out of the radical as

, which is equal to 2. It looks like this:

into

Changing \sqrt{4} to 2, we get the simplified result:

And that is as simple as you can go.
Hope that helped!
~Cam943