Hi there, you're welcome!

Okay open this image :

http://imgur.com/a/iKizjsO

First, good job for the number 2. Even if those lines touched others, you did well not changing their directions because those lines were delimiting other faces.

For the number 3, you missed an edge. Your intersection touched an edge of the box on the right, which was supposed the make the intersection deviate. There, I put 2 examples of what you could have done. They seem similar because the angle vary only slightly but in one example, the line I point is parallel to the edges of the box on the right and in the other example, the edge of the other box.

For the number 1, I broke my rule of the intersections needing to be parallel. I told you that rule to make things easier at first, but as you progress start breaking it. Honestly, you can redo that same example in many different ways. If the box on the right was totally behind the one on the left, there would have been no intersections. if the one on the left was slightly behind the one on the right, the intersections would have been totally different. It is about imagining which box is over which box, then trying to see how the faces would touch each other. Try different intersections with the same example :

1. The left box really in front of the right one, but still touching.

2. The right box really in front of the left one, but still touching.

3. Left box slightly in front of the right one.

4. The right box slightly in front of the left one.

It will be hard but since you're attacking your weakness, I am sure it will do wonders to your capacity of visualizing 3D space!

Keep up the good work!