$ a) (3x + 2)^3 + (2x - 2)^3 - 2x(x^2 + 12) $
$ =27x^3+54x^2+36x+8+8x^3−24x^2+24x−8−2x^3−24x $
$= (27x^3 + 8x^3 - 2x^3)+(54x^2−24x^2)+(36x+24x−24x)+(8−8)$
$= 33x^3+ 30x^2+36x$
$ b) (x + 2)^3 - x^2(x + 6) $
$=x^3+6x^2+12x+8−x^3−6x^2 $
$= (x^3 - x^3) + (6x^2 - 6x^2) + 12x + 8$
$ = 12x + 8 $