Analytic Geometry. finding the centroid? question on slope.

Hi, so im trying to find the equation of one median to find the centroid, but im stuck at trying to find slope because slope=6/0
here's my work so far;

MidpointXZ = B (0+8/2, 0+(-4)/2) = B(4,-2)
SlopeYB = 4-(-2)/4-4=6/0

this is where im stuck. is slope now undefined? what's the next step

thanks for your help!

It means that

You don't have to find the slope.

The coordinates of the centroid G are: