The center of the circle is the intersection of the perpendicular bisectors to the segments connecting these points: a) (7,5) and (-1,5); and b) (3.9) and (3,1). The perpendicular bisector to the segment a) is vertical line x = 3. The perpendicular bisector to the segment b) is horizontal line y = 5. Hence, the center of the circle is the point (x,y) = (3,5). From this point please complete the assignment on your own.