C3 super insane - second derrivatives - any help will be really appreciated

hi everyone just got some really hard (in my opinion obviously) questions.
this is my working:

a) find d^2y/dx^2 of:

y= (x^3 + 2x -1)^3

dy/dx= 3(x^3 + 2x - 1)^2 (3x^2 + 2) = (9x^2 + 6)( x^3 + 2x - 1)^2

d^2y/dx^2 = [18x( x^3 +2x -1)^2] + [ 2(3x^2)(x^3 + 2x - 1)(6x^2 + 4)]

using the product rule right?

but... the ans got : 6(x^3 + 2x - 1)(12x^4 + 18x^2 - 3x + 4)

soo yeah, got no clue how to factorise/simplify mine to get to theirs

I just done the first question, and your d^2y/dx^2 should be :

$[[color="Red"](9x^2 + 6)[/color]2(3x^2+2)( x^3 +2x -1)] + [ (x^3 + 2x - 1)^2(18x)]$

Ill leave it there to let you figure out how to get to the final answer. (Hint, you can take the factor x^3 + 2x - 1 out.)

Bold part (1) - I believe here you are diffrentiating the function in the brackets? If that's the case than it would be 3x^2 + 2

Bold part (2) - I'm not sure what you've done here, I think you've multiplied the function that you're taking the derivative of by 2 and diffrentiated. I think it would work if you left it as (9x^2 + 6)