Perpendicular bisectors and centres of circles

Hi hope someone can help me?

The question concerns three points A (3,1) B (-1,-11) and C (-5,9) that a circle passes through. I've managed to find the slope, midpoint and perpendicular bisector of AB (y=-x-14/3) and the same for AC(y=x+4). However when I try to find the centre and radius, I can't get the circles equation to balance. (The coordinates of each of the points A,B and C should balance to satisfy the equation).

Would be very happy if someone could point me in the right direction.

Many thanks

Stewpot