If the equation $3 x^2+10 x y+3 y^2+16 y+k=0$ represents a pair of lines, then the value of kis

If the equation $$a x^2+2 h x y+b y^2+2 g x+2 f y=0$$ has one line as the bisector of the angle between co-ordinate axes, then

The straight lines represented by the equation $$9 x^2-12 x y+4 y^2=0$$ are

If the equation $$k x y+5 x+3 y+2=0$$ represents a pair of lines, then $$k=$$