Description: Sal shows how to factor the expression 4x+18 into the expression 2(2x+9). Created by Sal Khan. What I want to do is start with an expression like 4x plus 18 and see if we can rewrite this as the product of two expressions. Essentially, we're going to try to factor this. And 18 is also divisible by 2, so we can rewrite 4x as being 2 times 2x.*Teacher Advisor is 100% free.