The circle is tangent to the line y=-5
by plotting the line you will know that the line has a point in (0,-5)
Point(0,5) to Point(0,-5) is the diamater of the circle by using the Midpoint formula((xsub1+xsub2)/2 or (ysub1+ysub2/2)) you will get the coordinates of the center.
5+(-5)/2 = 0
therefore the coordinates of the center is at (0,0)