One variable How to write the problem with 2 or more variables in one variable. Solution One way to do this is if you can express one of the two variables in terms of the other variable. So, for example, if you have a problem with variables x and y, you can write it just using x if you know the relationship between x and y. Here is an example. Let us say you have an equation that is originally 2x + y + 12 That has two variables. But if you know y is 3 more than x, you can express y as x + 3. Then your equation could be 2x + x + 3 = 12..