The center will be in the direct midpoint of the two points.
So, the formula for midpoint is (X1+X2)/2, (Y1+Y2)/2
Our X points are -3 and 7. So, we do -3+7/2, which is 2
Our Y points are 8 and 4. So, we do 8+4/2, which is 6
Put it into the form of a point, and we get (2,6) as the center of the circle.