Khan/khan-exercises — pull request #7644 by smenks13 (2011-12-03 04:41:28+00:00)
Title: New exercise: Systems of equations with substitution

@mwahl @maureen

Systems of equations with substitution as laid out in the Google doc. All comments and questions are welcome! Let me know if I can work on changing the elimination exercise to integer answers, or start on the "Solutions to Systems of Equations" card. Happy to help!