In the quadrilateral $ABCD$, the angles $B$ and $D$ are right . The diagonal $AC$ forms with the side $AB$ the angle of $40^o$, as well with side $AD$ an angle of $30^o$. Find the acute angle between the diagonals $AC$ and $BD$.
Problem
Source: V.A. Yasinsky Geometry Olympiad 2019 VIII-IX p3 [Ukraine]
Tags: geometry, cyclic quadrilateral, Angle Chasing, angles