Slope of tangent $= m _{ T }= m$
So, $m (-2)=-1$
$ \Rightarrow m =\frac{1}{2}$
Equation : $y = mx +\frac{ a }{ m }$
$\Rightarrow y=\frac{1}{2} x+\frac{3}{2 \times \frac{1}{2}}\left(a=\frac{6}{4}=\frac{3}{2}\right)$
$\Rightarrow y=\frac{x}{2}+3$
$\Rightarrow 2 y=x+6$
Point (5,4) will not lie on it