Linear inequalities2

Here is the sandcastle link: http://sandcastle.khanacademy.org/media/castles/kprobst:linearInequalities2/exercises/linear_inequalities_2.html

I took a stab at "Adding variety to multi-step inequalities" from the Trello board. This is my first pull request, so feedback is appreciated.

In particular:
- According to the wiki, the tests are broken, so I haven't yet written any tests. I'm happy to add tests once this is fixed.
- Are there additional changes I need to make to include these exercises on the knowledge map?
- I simply added a new file - if you think it's better to merge this with the existing linear_inequalities.html, just let me know.

Thanks!
Kathrin