Find the value of y for which the points

Let A(x1 = −3, y1 = 9), B(x2 = 2, y2 = y) and C(x3 = 4, y3 = −5) be the given points.
The given points are collinear if

$x_{1}\left(y_{2}-y_{3}\right)+x_{2}\left(y_{3}-y_{1}\right)+x_{3}\left(y_{1}-y_{2}\right)=0$

$\Rightarrow(-3)(y+5)+2(-5-9)+4(9-y)=0$

$\Rightarrow-3 y-15-28+36-4 y=0$

$\Rightarrow 7 y=36-43$

$\Rightarrow y=-1$