Ellipse

If the points of intersection of the ellipses $x^2+2 y^2-6 x-12 y+23=0$ and


$4 x^2+2 y^2-20 x-12 y+35=0$ lie on a circle of radius $r$ and centre $(a, b)$, then the


value of $a b+18 r^2$ is :