Would you use brackets in your test? In that case...
You multiply each number in the brackets by the other brackets for example: [ (x+y)(x+y) ] would equal [ x2 + xy + xy + y2 ]. Simplifying these expressions would equal x2 + 2xy + y2
Or...
As Skeeter said you combine the expressions from different sides to make a final answer.
4x+7y+2x+9y = 6x + 16y
These are purposely easier just for you to get the gist :)