Khan/khan-exercises — pull request #7749 by smenks13 (2011-12-04 20:15:53+00:00)
Title: New exercise: Systems of equations with elimination

@mwahl @maureen

I uploaded it as a separate exercise because I changed a lot of what was in the original code, but I can definitely overwrite the "Systems of Equations" exercise that's already out there after this has been reviewed and edited. Let me know what needs to be changed, thanks!