Answer: 
Step-by-step explanation:
The equation of the circle in center-radius form is:

Where the point
is the center of the circle and "r" is the radius.
Subtract 56 from both sides of the equation:

Make two groups for variable "x" and variable "y":

Complete the square:
Add
inside the parentheses of "x".
Add
inside the parentheses of "y".
Add
and
to the right side of the equation.
Then:

Rewriting, you get that the equation of the circle in center-radius form is:

You can observe that the radius of the circle is:
