What is the radius of the circle given by the equation below?

x2 + 2x = - y2 + 16y - 16

x² + 2x = - y² + 16y - 16

x² + 2x + y² - 16y = - 16

(x² + 2x + 4) + (y² - 16y + 64) = - 16 + 4 + 64

(x + 2) ² + (y - 8) ² = 52

(x + 2) + (y - 8) = 2√ (13)

The radius of a circle is 2√ (13).