I am sketching on a plane at a weird angle but I would like the line to be parallel to the top plane or Horizontal when viewed from the front.

(Solidworks 2018 file attached)

Please see image, I want to constrain them as horizontal when viewed from Plane 10 and sketching on Plane 11. I tried to convert and intersect entities but they don't work. I can't select the TOP Plane to make it parallel to it, and I tried drawing 3D Line on the Top Plane to make it parallel to it but the parallel condition is not what I want.

What is the easiest way to make lines horizontal when viewed from a different plane? 
Also, how do you intersect two planes with no sketches on them to get a sketch? (I want to get the centre line as well) I see the dashed line from the intersection of two planes but unable to convert it to a line.