a^2+b^2-6a-8b+25=0
(a^2-6a+9)+(b^2-8b+16)=0
(a-3)^2+(b-4)^2=0
a-3=0
a=3
b-4=0
b=4
b/a - a/b
=4/3-3/4
=16/12-9/12
=7/12