Find the center and the radius of the circle with the equation:
x^2 + 6x + y^2 + 4y + 12 = 0
a.

center: (3, 2)
radius: 1

c.

center: (6, 4)
radius: 12
b.

center: (-3, -2)
radius: 1

d.

center: (-6, -4)
radius: 12