`a)`
`(3-x)(9 +3x + x^2) + x (x^2 - 2)`
`= -(x-3)(x^2 + 3x + 9) + (x . x^2 - x . 2)`
`= - ( x^3 - 3^3) + x^3 - 2x`
` = - (x^3 - 27) + x^3 - 2x`
`= 27 - x^3 + x^3 - 2x`
` = 27 - 2x`
`b)`
`(x+2)^3 - x (x-4) (x+4)`
`= (x^3 + 3 . x^2 . 2 + 3 . x . 2^2 + 2^3) - x (x^2 - 4^2)`
`= (x^3 + 6x^2 + 12x + 8) - x (x^2 - 16)`
`= x^3 + 6x^2 + 12x + 8 - x^3 + 16x`
` = 6x^2 + 28x + 8`
`c)`
`(x+2)(x^2 - 2x +4) - (x^3 - 8)`
`= (x^3 + 2^3) - x^3 + 8`
`= x^3 + 8 - x^3 + 8`
` = 16`
`d)`
` (3-x)^3 - (x+3)(x^2 - 3x + 9)`
`= (3^3 - 3 . 3^2 . x + 3 . 3 . x^2 - x^3) - (x^3 + 3^3)`
` = (27 - 27x + 9x^2-x^3) - (x^3 + 27)`
`= 27 - 27x + 9x^2 - x^3 - x^3 - 27`
` = -2x^3 + 9x^2 - 27x`