have a polynomial that I need to find the zeros but I just want to know if I am going about it the correct way:

F(x)=x^4-3x^3-9x^2+27x

What I did was factored by grouping to get:

x^3(x-3)-9x(x-3)

(x-3)(x^3-9x) <<here i factored out an x to get x(x^2-9) and then i found the zero to be 3 for both. Is this correct? Any help is greatly appreciated