There are several ones like these i need to do but I should be able to do those if I can tackle this one. I have no clue where to start with this one.
It can be re-written as $\displaystyle 6 (2x + y)^2 - 13(2x + y) + 6$ which has the form $\displaystyle 6a^2 - 13 a + 6$. So factorise $\displaystyle 6a^2 - 13 a + 6$, substitute $\displaystyle a = 2x + y$ and simplify.