So our equation currently is ⇒

Let's first move all the constant to one side and group 'like variables' together:

Now lets complete the square of both equations

Now we know the circle's general equation format is:
⇒

- (h, k) ⇒ coordinate of the center of the circle
- r ⇒ length of radius of circle
Thus the radius of the circle is 7
Hope that helps!