Question 931563
For a line in the general form, 

{{{Ax+By+C=0}}}, 

{{{m=-A/B}}}

so 

{{{m[1]=-4/(-1)=4}}}

and

{{{m[2]=-1/(2k)}}}

we require that
{{{m[1]m[2]=-1}}}

therefore...

{{{-4/(2k)=-1}}}

so


{{{k=2}}}