Find the missing angle in the following figure.

The correct option is B ${135}^{\circ }$

${15}^{\circ }+{30}^{\circ }+x={180}^{\circ }$
${45}^{\circ }+x={180}^{\circ }$
$x={180}^{\circ }-{45}^{\circ }$
$x={135}^{\circ }$