Ok for the first one I did this:
$\displaystyle (x+2)(x+4)$ = $\displaystyle x^2+4x+2x+6$ = $\displaystyle x^2+6x+6$
$\displaystyle x^2-(x^2+6x+6)$
$\displaystyle x^2-x^2 = 0$
So we left with $\displaystyle 6x+6$
EDIT: I'm thinking that maybe when joining 4x and 2x together, you multiply them together? so 8?