Derive the Equation of a Circle Practice Test

Which equation follows from the geometric definition of a circle for the set of all points $(x,y)$ that are a distance $6$ from the center $(1,-3)$?

The equation $$x^2 + y^2 - 8x + 6y + 9 = 0$$ represents a circle. After completing the square, what are the coordinates of the center and the radius?