If $\;\overrightarrow{x}=3 \hat{i}-6 \hat{j}-\hat{k}\;, \overrightarrow{y}=\hat{i}+4 \hat{j}-3 \hat{k}\;$ and $\;\overrightarrow{z}=3 \hat{i}-4 \hat{j}-12 \hat{k}\;$ , then the magnitude of the projection of $\;\overrightarrow{x} \times \overrightarrow{y}\;$ on $\;\overrightarrow{z}\;$ is :

Question

$(a)\;12\qquad(b)\;15\qquad(c)\;14\qquad(d)\;13$