I'm currently stuck on 2 problems.

$\displaystyle 4(3-x)^2-(3-x)^3+3(3-x)$ I got $\displaystyle 3-x(6(3-x)(3-x)^2)$

That doesn't seem right but what went wrong.

also

$\displaystyle 15(2z+1)^3+10(2z+1)^2-25(2z+1)$ => $\displaystyle 5(2z+1)(3(2z+1)^2+2(2z+1)-5)$ => $\displaystyle 5(2z+1)((2z+1)^2(2z+1))$

which also doesn't seem right.