The center of the circle is expressed as (h,k) in the standard form of equation. In this case, the diameter endpoints are (-3, 8) and (7, 4). Hence the circle center has coordinates which are the midpoints of the two points.
x = (-3 + 7) /2 = 2
y = (8 + 4) /2 = 6
hence the center of the circle is (2,6)
