In the figure below, the circle with centre $o$ has $OA = 4$ and $BC =2$, What is the value of $x$? <br><br>

Question

$\begin{array}{1 1} (a)\; 15^{\circ} \\ (b)\; 30^{\circ} \\ (c)\; 45^{\circ} \\ (d)\; 60^{\circ} \end{array}$