(4-a)^2+(1-b)^2=r^2 = (6-a)^2+(-3-b)^2
a-2b = 7
(6-a)^2+(-3-b)^2=r^2 = (-3-a)^2+(0-b)^2
a=1/3b+2
b= -3
a= 1
r=5