Description: Sal solves the equation 20 - 7x = 6x - 6. Created by Sal Khan and Monterey Institute for Technology and Education. And then we'll put all the x terms, the negative 7x and the 6x, we'll put it all on the left-hand side. So to get the 20 out of the way from the left-hand side, let's subtract it. Let's subtract it from the left-hand side.*Teacher Advisor is 100% free.