D. (8, -4)
Since SW is the diameter of the circle, the center of the circle should be right in the center of that line. You simply have to find the midpoint of the line
Midpoint formula:
[ (x1+x2)/2 , (y1+y2)/2 ]
After substituting numbers:
[ (6+10)/2 , (-1-7)/2 ]
[ 16/2 , -8/2 ]
=(8, -4)
~~hope this helps~~