Answer:
Center: (3,3)
Radius:

Explanation:
Midpoint and Distance Between two Points
Given two points A(x1,y1) and B(x2,y2), the midpoint M(xm,ym) between A and B has the following coordinates:


The distance between both points is given by:

Point (5,7) is the center of circle A, and point (1,-1) is the center of the circle B. Given both points belong to circle C, the center of C must be the midpoint from A to B:


Center of circle C: (3,3)
The radius of C is half the distance between A and B:


The radius of C is d/2:

Center: (3,3)
Radius:
