The following set of the three vectors

$$\begin{pmatrix} 1\\2\\1 \end{pmatrix}, \begin{pmatrix} x\\6\\x \end{pmatrix}\:and \:\begin{pmatrix} 3\\4 \\2 \end{pmatrix},$$

is linearly dependent when $x$ is equal to

1. $0$
2. $1$
3. $2$
4. $3$