In the adjoining figure $ABCD$ is a $\parallel$ gm which $\angle BAD=75^{\circ}$ and $\angle DBC =60^{\circ}$, calculate $\angle CDB$

Question

$\begin{array}{1 1} 40^{\circ} \\ 70^{\circ} \\ 75^{\circ} \\ 45^{\circ} \end{array} $