The length of the line that connects two opposite vertices in a concave quadrilateral

Question

Let $ABCD$ be a concave quadrilateral where $B$ is the reflex angle and $D$ is the opposite angle.Let the length of segments $AB$ and $BC$ be $10$ and the length of segments $AD$ and $CD$ be $15$. What's the length of the segment that would connect $B$ and $D$? I tried to make a kite and use the area of the kite to find the area of the concave quadrilateral but I didn't succeed. Thanks!