have you seen things of circles and triangles and squares? This problem is just like this. You would probably identify the squares circles and triagnles as...well....traingles circles and squares. Well, we do that but with the variables.
The numbers with 'x' is one group. And the one without it is another group. So....take 'x3' and take the x9. Because they have the same variable.
x3 + x9. (why we are adding is because it has nothing to drag with it and both of these numbers are positive)
x12!
Now do teh same with 15 and 3. Bring the plus and the subtraction sign with 3 and 15. We cant just leave them there. 15-3=12.
