What is the center and radius of the circle with the equation x2 + y2 – 10x – 12y + 36 = 0 ?

X² + y² - 10 x - 12 y + 36 = 0
( x² - 10 x + 25 ) + ( y² - 12 y + 36 ) - 25 - 36 + 36 = 0
( x - 5 )² + ( y - 6 )² = 25
( x - 5 )² + ( y - 6 )² = 5²

The center:  ( 5, 6 ),  the radius:  r = 5 

Hnmmmn not sure