First plot those points. You should see a *right* triangle, with sides:
4 vertical and 6 horizontal
So, the circumcenter is the mid point of the hypotenuse of the triangle, because it is a right triangle (otherwise is really harder).
The mid point of F and E:
CIRCUMCENTER = (F+E)/2 = ( (1,5)+(7,1) ) / 2 = (8,6)/2 = (4,3)
ANSWER (4,3)