1. -4/3, I just graphed it in desmos and fiddled with some stuff.
2. So the distance of the Center, (x,y), to B and A are the same.
We know that y is 5 from tangent rules.
(x,5)
The distance from (x,5) to (9,0) is x, since to B is also x
\(\sqrt{(9-x)^2+25}=x\)
\((9-x)^2+25=x^2\)
\(x^2-18x+106=x^2\)
\(x = \frac{53}{9}\)
\((53/9,5)\)