in the equation y = 2x + 4, you know that the gradient is 2 (the number before x).
for a perpendicular line you need the negative reciprocal of 2, which is - [tex] \frac{1}{2} [/tex] .
you then need to use the equation
y - [tex] y_{1} [/tex] = m(x - [tex] x_{1} [/tex] )
substitute in your coordinates:
y - -2 = - [tex] \frac{1}{2} [/tex] (x - 3)
simplify:
y + 2 = -0.5x + 1.5
rearrange:
y = - [tex] \frac{1}{2} x[/tex] - [tex] \frac{1}{2} [/tex]
