If x =3 i -6 j - k, y = i +4 j -3 k and z =3 i -4 j -12 k, then the magnitude of the projection of x × y on z is:

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