Angles · Challenge problem

Four rays $OA$, $OC$, $OB$, $OD$ come out of point $O$ in that order (so $OC$ is between $OA$ and $OB$, and $OB$ is between $OC$ and $OD$). Angle $AOB$ and angle $COD$ are both right angles, so they overlap. The whole angle $AOD$ measures $150^\circ$. How many degrees is angle $COB$, where the two right angles overlap?