Answer :
Let:
[tex]y=ax[/tex]The equation which represents a direct variation. where a is the constant of proportionality.
[tex]\begin{gathered} x=3,y=6 \\ 6=3a \\ a=\frac{6}{3} \\ a=2 \end{gathered}[/tex]Therefore:
[tex]\begin{gathered} x=k,y=4 \\ 4=2k \\ solve_{\text{ }}for_{\text{ }}k\colon_{} \\ k=\frac{4}{2} \\ k=2 \end{gathered}[/tex]