Graph the surfaces  y= x + z and y = 1 - z on the same axes using the domain |x| < or = 1.2 , |z| < or = 1.2 , and observe the curve of intersection of both surfaces. Show that the projection of this curve onto the xz-plane is an ellipse.

So that's that problem. I am so lost on what to do. I know it has to do something with implicitplot3d.