What is the radius for a circle whose equation is x2 + y2 = 64

Find the center and radius of each circle:
x2 + y2 = 36 
The standard form for a circle with center at (h,k) and radius r is: 

(x-h)^2 + (y-k)^2 = r^2 
Since x^2 + y^2 = 36 is the same as: 
(x-0)^2 + (y-0)^2 = 6^2 
this cicle has center (0,0) and radius 6.

That they are numbers and related to each other.

Then just do it (lol)