I know the method like this

$36=2 \times {\color{Red}{2 \times 3} } \times 3 $

$6={\color{Red}{2 \times 3 } }$

Less than can’t be possible and multiple of $’6’$ which is less than or equal to $’36’$ is also not possible because $36$ is a multiple of $6$.

So, $k=6,42$ is possible.