Answer: 10 units.
Explanation:
The equation of the circle in Center-radius form is:

Where the center is (h,k) and "r" is the radius.
The equation of the circle given is:

You can observe that is written in Center-radius form.
Then, you can identify that:

Knowing this, you need to solve for "r" to find the lenght of the radius.
This is:

Therefore, the lenght of the radius is 10 units.