The center of a circle is at (-5, 7) and its radius is 6 units. which of the following is the equation for this circle? a) (x - 5)2 + (y + 7)2 = 36 b) (x + 5)2 + (y - 7)2 = 36 c) (x - 5)2 + (y + 7)2 = 12 d) (x + 5)2 + (y - 7)2 = 12