This is a video explanations of how solve linear equations with variables on both sites by KhanAcademy. It will come in useful for anyone who is stuck with this kind of equations or have to explain to a kid how to do it. Personally I used it for the latter when working on math tests for official webpage (http://yourhomeworkhelp.org/do-my-programming-homework/ ) and had to figure out how to point the learners into the right direction.