Question 3
The convex quadrilateral $ABCD$ has $\angle CAD=40^\circ$, $\angle BAC=50^\circ$, $\angle CBD=20^\circ$ and $\angle CDB=25^\circ$, as shown in the diagram below. If $O$ is the intersection of $AC$ and $BD$, what is the measure, in degrees, of $\angle AOB$?
