Perform the indicated operations on the following vectors:
$$\begin{aligned}
&\vec{a}=2 \vec{j}+\vec{k}, \quad \vec{b}=-3 \vec{i}+5 \vec{j}+4 \vec{k}, \quad \vec{c}=\vec{i}+6 \vec{j},\\
&\vec{x}=-2 \vec{i}+9 \vec{j}, \quad \vec{y}=4 \vec{i}-7 \vec{j}, \quad \vec{z}=\vec{i}-3 \vec{j}-\vec{k}
\end{aligned}$$
$$4 \vec{z}$$