Okay, I can't guarantee if I have understood the question perfectly, but here's what I came up with:
Plane 1
normal vector = CA x BA = (0,1,5) x (1,1,8) = (3,5,-1)
So the equation can be written as 3x+5y-z+k=0.
Since it passes point B, 3(1)+5(1)-(8)+k=0, so k=0. (3+5-8+k=0)
The...